Special Design Issues for Sports Games

Sports games face a number of design issues that are either rare or irrelevant in other kinds of games.

Physics for Sports Games

During play, your game will be running a physics engine that determines the behavior of moving bodies in the match. The physical behavior of an inanimate object such as a baseball is comparatively easy to implement. The physical behavior of humans , however, is much more complicated. Early sports games tended to treat a running athlete rather like a rocket: She had a velocity vector that gave the speed and direction of her movement, and an acceleration vector that gave the force and direction with which she was pushing. Modern sports games have much richer simulations with a great many variables , taking into account such things as the friction coefficient of the playing surface ”for example, rain and snow make fields slippery and reduce traction.

Designing the physics simulation for a sports game is a highly technical problem and is beyond the scope of this book. However, we offer one caveat: Because a sports game is a simulation of the real world, it is a common error to think that the physics in a sports game should be as realistic as possible. They shouldn't be, for two reasons:

First, the player is not actually running around on the playing field herself; she is sitting in a chair , watching a screen, and controlling an athlete through a handheld controller. She has neither the immediate experience of being on the field nor the precise control over her movements that a real athlete does.
Second, the player is not a professional athlete. There is a good reason why only a small number of people are capable of hitting a baseball pitched at 95 miles per hour . The length of time that the ball is within reach of the bat is about 0.04 seconds. It's simply not realistic to expect that an ordinary person, looking at a video screen without the benefit of depth perception, could react that fast.

For both of these reasons, it's necessary to fudge the physics to make the game playable . We slow the pitch so that the batter has a reasonable chance of hitting it, and we artificially adjust the position of the bat so that it intersects the path of the ball. It doesn't matter whether the physics perfectly copy the real world as much as whether they seem to be producing a reasonable simulation of the sport as it is played by professionals. Even in a highly realistic game, your objective is to provide an enjoyable experience, not a mathematical simulation of nature.

Rating the Athletes

One of the biggest tasks you have in designing a sports game is developing a rating system for the skills and athletic abilities of all the athletes in the game. The rating system provides the raw data that the physics engine needs to simulate the behavior of the athletes accurately. As your programming team develops the physics engine and game AI, you should work with them to determine what ratings are needed. Researching the athletes' performance and setting the ratings for them is a task that can take many months, and you will probably want to delegate it to junior designers or assistant producers .

In most team games, the athletes have one set of ratings common to all of them, plus specialized ratings that apply only to athletes playing a particular position.

Common Ratings

These are examples of the kinds of ratings that might be common to all the athletes in a game:

Speed. The athlete's maximum moving (running or skating or swimming) speed under ideal conditions.
Agility. A measure of the athlete's ability to change directions while moving.
Weight. Simply the athlete's weight, which affects the force he transmits in a collision and the inertia he has when struck by someone else.
Acceleration. The rate at which the athlete can reach top speed.
Jumping. The height to which the athlete can jump.
Endurance. The rate at which the athlete gets tired during the course of the game.
Injury resistance. The probability that an athlete will be injured.

Specialized Ratings

These ratings apply to a specific position ”in this case, the quarterback in American football:

Passing strength. The distance that the quarterback can throw the ball.
Passing accuracy. The precision with which the quarterback can throw the ball.
Dexterity. The quarterback's general dexterity in handling the ball. This affects his chances of dropping the snap or fumbling a handoff .
Awareness. The quarterback's ability to sense that he's about to be tackled and to try to get out of the way.

Athlete AI Design

The AI in most computer games is rather crude. In action games and first-person shooters, the player's AI-driven opponents typically have a small number of behaviors triggered by specific events (appearance of the player on the scene, being shot at, and so on). When they're together in a group , they very seldom act in concert or assign special roles to particular individuals, nor do they help each other. It's every monster for itself. When there are no stimuli, they go into a simple idle loop, walking aimlessly around or standing still.

These kinds of actions aren't acceptable in a sports game. People don't mind if a monster in a first-person shooter wanders randomly around, but the athletes in a sports game must behave like humans, and that means deliberate , intelligent action. Particularly in team games, each athlete is working with the others on the team to accomplish particular goals. The position the athlete plays dictates behavior to some extent, but within those boundaries, the athlete still has to respond intelligently to a number of possible events. In a relatively simple sport such as tennis, there might not be many of these events, but in a highly complex sport such as American football, with 22 players on the field at a time, there can be hundreds.

Defining the State Space

The best way to design sports-game AI is to map out a game's states as a giant flowchart. There could be far more states than you realize at first. Corner kick in soccer is not just one state, but several. There is the period before the ball is kicked, after it has been kicked but has not yet touched another athlete, after it has been touched by another athlete, and so on. See Figure 12.2 for a partial example.

Figure 12.2. A flowchart detailing part of the "corner kick" situation in soccer.

graphics/12fig02.gif

Consult the official rules of the sport as you construct the flowchart: They will often describe states in detail, with special rules applying to each. However, the rules alone are not enough; they describe game states for the purposes of listing legal and illegal actions, but not for tactics or strategy. Whenever something changes that requires the athletes to adopt a different tactic, the game has moved into a different state.

Setting Collective and Individual Goals

After you define the game states, you can start thinking about what the team should do in that state ”where each athlete should be trying to go and what he should be trying to do to support the team's collective goal at that moment. In some cases, these activities are defined with reference to a specific individual on the opposing team, trying to prevent him from doing his job. The software must have a way of matching up athletes with their opponents, just as the real athletes do.

When you have defined what the team should be trying to accomplish in a particular state and have assigned each athlete a role, you then must define exactly how the athlete is to perform that role: what direction he moves, what other movements he makes, which animations should be displayed, and so on. If the role is a defensive or supportive one, such as covering an opposing athlete, the individual AI for it might still be fairly complex. For example, a soccer player dribbling the ball might make a feint, trying to fool his opponent into thinking he's passing the ball. The software knows perfectly well that this is a feint, but sometimes the defender should be fooled and sometimes he shouldn't, depending on his awareness rating and, in either case, how he responds.

An athlete with nothing to do shouldn't just stand still. Most sports games include fidgets , short animations in which the athlete shifts his weight, stretches his arms, or makes some other neutral action every few seconds. Even if play is underway but the athlete is not closely involved ”the third baseman on a fly ball to right field, for example ”he at least should turn and watch the action.

Injuries

Injuries are a sad but common side effect of sports, and serious simulations take them into account. Because they occur somewhat randomly, they're outside the player's control and can be frustrating. Most sports games allow the players to turn off injuries if they don't like the effect that they have on the game.

Although it's possible for an athlete to injure herself simply by running or jumping, this doesn't provide the player with any visible explanation for why the injury occurred. A lot of sports games therefore limit injuries to cases in which there has been a collision of some kind, usually between two athletes. To determine whether an injury has occurred, you should include such factors as the relative speed of the two athletes, their weights, their respective susceptibilities to injury, and a random factor. The heavier an athlete is, the more force she imparts in a collision, and it is the force that does the damage to the other athlete.

Some positions , such as the pitcher in baseball, are simply so stressful that they can result in injuries without a collision, especially the longer the pitcher stays in the game. You can compute the probability of an injury on every pitch and raise it slightly with each one.

You can also decide which part of the body sustained the injury and the length of time for which it will disable the athlete. Study reports of injuries and recovery times for the sport you are simulating. If your game tracks athletes over a period of time, you will have to consider the cumulative effect of injury and recovery time on their careers.

Arcade Mode Versus Simulation Mode

Arcade mode versus simulation mode is a realism switch that lets the player adjust the behavior of the game to suit his tastes. Arcade mode makes the game more exciting at the expense of realism ; simulation mode makes it a more accurate simulation of the real sport at some expense in fun. For example, in baseball, an athlete is doing well if he has a .333 batting average ”that is, gets a hit only one time in three. Some players might find that a little dull. Switching the game to arcade mode could let the player get a hit 50 percent of the time or even more. It skews the play toward lots of action and relatively few strikeouts or walks. In American football, you could artificially increase the number of completed passes by improving the quarterback's throwing accuracy and the receiver's catching skills.

To implement arcade mode, you'll have to decide what sort of changes to the real game would make it more exciting. If you want your game to have both arcade and simulation modes, we recommend that you start with the serious simulation first and then design the "fudges" that make it arcadelike. Serious simulations are much more difficult to tune, and it's important to get them right first. If you start with an arcadelike design and then try to make it serious, you might never get it right.

Simulating Matches Automatically

Sports games that can play an entire season for a whole league of teams often provide a means of simulating matches automatically, without the player having to play them. For example, each team in professional baseball plays 162 matches in a season . With 30 teams and 2 teams in each match, this is a total of 2,430 matches ”only the most rabid fan would want to play them all personally . To generate results for matches that the player doesn't play, you need a way of simulating a match. Of course, you'll want the resulting scores to accurately reflect the relative strengths of the teams: A bad team should be able to beat a good team occasionally, but not often.

Computer Versus Computer

The simplest way to simulate matches automatically is to let the computer play out the match in computer versus computer mode, as described in the section, "Competition Modes," earlier in this chapter, and record the results. If the game's simulation model is good, it should produce scores that reflect the real abilities of the competitors . Unfortunately, this is a slow way to do it. If the player wants to generate results for a match that she doesn't really care about, she probably wants it done quickly.

Simulation Without Graphics

One solution is to simulate the whole match exactly as in computer versus computer mode, but to turn off the graphics so that nothing is displayed. Because displaying the graphics often takes up the majority of the computer's time, an entire match can be simulated in a few seconds. Electronic Arts' Earl Weaver Baseball game did this successfully. It makes the programming more complicated, however, because throughout the whole program, there have to be checks to see if the game is in simulation mode or display mode. When you do this, test the game to be sure that the results without graphics are the same as those with graphics.

Faking It

The alternative many games adopt is to fake it ”in effect, to roll dice to generate game scores. The dice are loaded somewhat so that good teams get high scores and bad teams get low ones, and whichever team rolls the highest score wins the match. You will need to devise a suitable algorithm for generating point values: In games such as American football and rugby, in which different numbers of points are awarded for different kinds of scores (touchdown, field goal, and so on), certain score values are much more common than others. It's extremely rare, for example, for a team to end an American football game with a score of 2. You'll also need to make sure that your algorithm creates a reasonable random distribution; no professional soccer game should ever end with a score over about 15.

One disadvantage of this dice-rolling technique is that it doesn't generate any other statistics besides the scores themselves . In a particularly statistics-rich sport such as baseball, if you don't generate performance data for each individual player, some fans will consider your game to be a lightweight, not a serious, simulation. It's up to you to decide just how important that market is to you and how much effort you're prepared to exert to meet their expectations.

Licenses, Trademarks, and Publicity Rights

Many years ago, small developers could make and sell computer games using names such as "NFL" and get away with it, because the National Football League never knew it was happening. You can't do this now. Interactive entertainment is big business, and you have to be scrupulously careful to avoid violating trademarks or personal publicity rights.

Team and League Trademarks

The exact details vary from league to league and country to country, but generally in America, the name, logo, uniform design, and other indicia of all the teams in a league, plus the name and logo of the league itself, are licensed for use by the league. You, or your publisher, will have to negotiate an agreement with the league to use these symbols in your game. Before Electronic Arts signed an agreement with the NFL, early versions of John Madden Football referred to teams only by their town names (such as San Francisco or Chicago) rather than by their team names (the 49ers and the Bears) and did not show any logos. The colors of the uniforms were similar but not exactly the same. You can pull this trick, too, if you dare, but you're risking a lawsuit if you get too close.

Individual sports, such as gymnastics or figure skating, are often governed by a variety of bodies in different countries around the world. The names and indicia of particular events, such as the Kentucky Derby, are owned by the organizations that produce them ”in this case, the Churchill Downs racetrack. In recent years, these groups have begun to exploit their intellectual property rights in a variety of ways, so they tend to come down hard on anything that seems to be an infringement. Don't assume that just because an event has been around for decades, you can freely use its name.

Personal Publicity Rights

You cannot use the name or photograph of a real athlete without permission. An athlete's name and likeness are part of his personal publicity rights, and, of course, famous athletes sell the rights to use their names for millions of dollars when they endorse a particular product as an individual. You might need to negotiate with an organization that licenses the rights to use all the players' names collectively. This might be the league, in some cases; in others, however, including the NFL and Major League Baseball, you have to contact the athletes' unions. And unless you have the endorsement of a specific athlete, you must make sure that your game displays all athletes in approximately the same way, or endorsement could be implied . You can't make it look as if an athlete has endorsed your game when that's not the case.

Photographs present further difficulties. You must obtain a license from the person in the photograph and also from the person who took the photograph: the photograph's copyright holder. Again, some governing bodies have special clearinghouses for these kinds of things: NFL Photos is a special department of the NFL that licenses still photos for all the photographers who are accredited to take pictures at NFL matches. The license, however, does not grant you the personal publicity rights of the athlete in the picture; you have to obtain those separately. You can also license photos from the trading card companies, as well as from journalistic bodies such as the Associated Press, and from private photo libraries.

In short, the whole issue of rights in sports games is a legal minefield. Nowadays, even the stadiums might claim special rights, and many stadium owners auction the name of the stadium to the highest bidder, as with 3Com Park in San Francisco. As a designer, you probably won't have to deal with obtaining all these licenses yourself, but you should know that it's not safe to specify simply that a game will use all the team and player names and photos. Obtaining them and the right to use them is a very costly and time-consuming business. It's best to design the game in such a way that it doesn't depend on having these things, unless you're certain that they will be available.

Audio Commentary

Most sports games try to reproduce the experience of watching the sport on television. An important part of that experience is hearing the announcers' commentary, or play-by-play. Most TV and radio sports broadcasts include at least two people, the play-by-play man and the color commentator . The play-by-play man describes the play on a moment-by-moment basis. The color commentator, usually a retired coach or player, offers insights about strategy and tactics, as well as background material on the teams or individual players. A third voice that you occasionally hear is that of the stadium announcer over the public address system. His remarks tend to be quite formulaic, although they do occasionally include requests to move misparked cars , retrieve found children, and so on.

Defining the Events to Describe

A good way to size up the job of duplicating the audio experience is to record a TV broadcast of a real match and then transcribe everything that is said and by whom. Do this for two or three matches, and you will begin to notice patterns in the play-by-play: The announcers tend to announce the score at particular times, they use certain repetitive language, and so on. As you watch the match on videotape, take note of the different kinds of events that occur and the different remarks they elicit from the commentators. The color commentator's events aren't the same as the play-by-play man's. The color commentator speaks at more dramatic moments, or when an athlete has done something particularly spectacular (or particularly bad). For example, in tennis, you might have a color comment like, "She's having a terrible time with those double faults" when an athlete commits four double faults in a single game. Be sure you play it only once, however ”not on every subsequent double fault.

When you have a set of match events that you want to create commentary for, sit down with the programmers and discuss them to make sure they are detectable. Some, such as a strikeout in baseball, will be uncomplicated, but a lot of them will be judgment calls. For example, a dropped pass in football that the player really should have caught is not so easily detectable; you can detect the dropped pass, but what determines whether he should have caught it? It must be calculated from such things as the receiver's dexterity rating and the accuracy with which the pass was thrown in the first place ”provided that it wasn't tipped away by a defender. It's always best to err on the side of caution in these cases: Don't design judgment calls that the player is likely to disagree with, or he'll think your game is stupid. As the saying goes, "It's better to remain silent and be thought a fool than open one's mouth and remove all doubt."

Don't forget the introductory and wrap-up material at the beginning and end of the match ”for example, "Welcome to Mile High Stadium for today's game between the New England Patriots and the Denver Broncos. It's a cold and windy day."

Writing the Script

When you have established the events that need audio commentary, you can start to write the audio recording script that will implement it. For each event, you will typically want to record four or five variant comments so that the players don't hear the same thing every time the event occurs. Obviously, the more comments you can write per event, the better your game will sound. The number of comments is really limited only by the available space on the distribution medium and the number of things you can reasonably think of to say about a given event.

As you write the script, you will discover places where a name or number will need to be included, usually the names of athletes or teams or the current score. If the sport is one with a large number of athletes, you cannot afford to record the sentence with every possible athlete's name in it. Instead, you will need to record the sentence as a whole using a sample name and edit the resulting audio file into clips, one part before the name and one part after. Your programmers must devise a method of streaming the sound clips, inserting the correct name in the right place in such a way that they sound seamless. When you record the sentence , use a sample name that begins and ends with a T or a K sound so that it doesn't slur into the rest of the sentence and so that it can be cut cleanly. For example, "Merrick steps up to the free throw line" enables the engineer to cut between Merrick and steps , whereas "Rogers steps up to the free throw line" would produce a slur from Rogers into steps .

Whenever possible, you should try to write the script in such a way that names are at either the beginning or the end of a sentence. You can then have your voice talent record the names of all the athletes who appear in the game. Each name will need to be recorded twice, once using the voice inflection for the beginning of a sentence, and once at the end. Don't try to record the names by themselves; record a complete sentence and then throw away all but the name, for example, "Thomas takes it" and "I'll pick Thomas." Again, using the T and K sounds adjacent to the name allows a clean cut in the audio.

Case Study: Madden NFL Football

Madden NFL Football is one of the longest-established and best-selling game franchises in the history of our industry. From its earliest beginnings on the Apple II, it has grown into a financial powerhouse that produces a new edition on several different platforms every year and makes millions of dollars for its publisher, Electronic Arts. Versions of Madden have appeared for personal computers and every major console machine ever produced.

Madden is not redesigned every year, nor is its code rewritten. Its artwork and video sequences are updated, and it gets new features each year, but it undergoes a complete overhaul only every four or five years ”often when a new generation of game console appears. The majority of the design work each year consists of tuning and improving the gameplay and adding more features. These features expand the "football experience" to include aspects of the sport that go beyond playing a single match against another team. Among them are the following:

Ability to hire and trade players among teams, subject to the limitations of the salary cap established by the NFL.
Participation in the NFL draft.
Detailed performance statistics on players.
Season, tournament , and practice modes.
Franchise mode, letting players take a team through several seasons in an effort to build a dynasty.
A play editor, allowing players to customize their playbooks.
Madden University, which includes detailed tutorials about offensive and defensive strategies, commentaries on the strengths and weaknesses of each team, and historical background.
Adjustable AI, enabling players to set the coaching stances of computer-controlled teams to aggressive , neutral, or conservative.
Arcade mode, a simplified and exaggerated form of the game.

As you can see, even though the sport itself changes little from year to year, new features and details can always be added to a sports game.

By far, the largest single task in developing Madden every year is research: rating the skills of the real players who appear in the game, keeping track of which team they're playing for, finding photographs of them, and so on. In addition to researching the players, the production team must research the coaches ”trying to find out what kinds of plays they like to run, whether they're aggressive or conservative, and so on. The team's playbooks must be updated every year to reflect changes in coaching practice, and the new plays must be tested to make sure that they're effective but not unstoppable.

In short, Madden is a highly successful sports game that offers its players a wide range of playing styles, from the quick and easy arcade game to the detailed minutiae of designing plays and adjusting rosters. As a game that tries to "do it all," it's well worth studying .

Other Peculiarities

The following sections detail a few other issues peculiar to sports games.

Invented Sports

From time to time, someone tries to create a sports video game of a completely invented sport, as opposed to a take-off of an existing one. Empire Interactive's Speedball 2100 was one such game. Experience shows, however, that this is a risky enterprise. Hardcore sports gamers are seldom interested in completely new sports; they'd rather play a game that simulates a sport that they're already familiar with. Other types of gamers aren't that interested in sports games anyway and aren't very likely to want to play a one-off sports game unless it appeals to them for some other reason. If you're thinking of inventing a new sport specifically for a video game, we advise you to design it as a video game, without concerning yourself with what it might be like in the real world. This is how Speedball was designed; although it was theoretically a sport, it included powerups and other arcade-game elements to make it more interesting.

As we said earlier, one of the trickiest aspects of sports game design is mapping real-world activities to a limited input device. Players are willing to tolerate some awkwardness in the user interface when it's a real sport because they understand the problems. With an invented sport, they're unlikely to be so generous. When designing a completely new sport, you might consider working backward from the controller to the sport itself, designing around the limitations of your hardware.

Instant Replay

Instant replay is now an essential part of watching sports on television, so naturally video game players want it as well. It's not difficult to design, although it might be difficult to implement. Your game will need to keep track of the exact position and animation step of every player and other key objects on the field in each game frame. When the player requests an instant replay (usually through a pause menu), the game can play them back. Of course there is a limit to how much of this information you can keep around, and some natural boundary is likely to suggest itself ”in baseball, the time since the most recent pitch; in American football, the time since the ball was snapped. In continuously flowing games such as basketball , you might have to establish an artificial time limit.

The best instant-replay mechanisms allow all the following features for maximum flexibility:

Play, stop, fast-forward, rewind, and single-frame advance and reverse operations, to allow the player to see exactly what happened at every instant.
The ability to move the camera in all three dimensions.
The ability to pitch the camera up and down, and turn (panning) it left and right.
The ability to lock the camera to a given athlete or the ball, to follow something wherever it goes. This is usually done by showing a symbol on the ground that represents the camera's focus of attention. If the symbol is directly under an athlete's feet when the player stops moving the camera, the camera locks onto that athlete.

Instant replay lets the players see the action from perspectives that they can't use when actually playing the game. For the game's publisher and developer, it's an invaluable tool for grabbing dramatic screen shots or gameplay footage for sales and demonstrations . You should consider it an essential feature of any sports game that you design.

Camera Difficulties in Games with Widely Separated Action

In most sports, the focus of the action is in one location. In a race, it's on the leaders . In any soccerlike sport (soccer, hockey, basketball, water polo, and so on), it's on the object that's supposed to go into the goal; similarly, in any tennislike sport, it's on the ball. Baseball and cricket are unusual in that the action takes place in two places at once: where the ball is and also where the runners are. In baseball, this can be as much as 400 feet away. You can't show both the runners and the ball without zooming out to a blimp view so high up that nobody can see anything clearly.

To solve this, most baseball video games implement a picture-in-picture solution: The camera follows the ball, but a small diagram of the baseball diamond in one corner of the screen shows the positions of the runners, often as no more than colored dots (see Figure 12.3). When a runner reaches a base, his dot changes color to indicate that he is safe. The player controlling the fielders watches the main screen, and the one controlling the runners watches the diagram (keeping one eye on the main screen to see if the ball is coming). Because cricket has only two stumps instead of four bases, this arrangement is even easier.

Figure 12.3. 3DO's High Heat Baseball . Note the inset showing player positions. The round dots adjacent to the bases are runners taking their leads.

graphics/12fig03.gif

Home-Field Advantage

Considerable debate has raged over the years about whether to build a home-field advantage into sports games. Although the home-field advantage is statistically significant in a number of sports, we recommend against it. Players like to feel that they are playing a fair game, and if they know that the odds are artificially stacked against them whenever they play an "away" game, they will resent it. It's also unclear exactly how the home-field advantage should be implemented. The phenomenon is normally observed from win-loss statistics, but, of course, the computer can't simply turn a loss into a win. It could shave off a percentage of goal-scoring attempts, but even this is likely to have odd side effects. If a scoring attempt that clearly should have succeeded fails for no visible reason, the players are bound to notice it.

Sports Game Worksheet

In designing a sports game, consider the following questions as a starting point:

What sport am I simulating? Is it a real sport or a made-up one? If it's real, do I want to get a license from a governing body?
What are the rules of my sport? If it's a real sport, can I really implement them all, or will it have to be a subset?
What competition modes am I going to offer ”single-player, competitive, cooperative, teams? Which ones make sense for my sport, and which don't?
In addition to playing a single match, what other game modes will I offer? Season, tournament, franchise, career?
What is the best perspective for playing my sport? Directly overhead, from the sidelines, from some other angle? What intelligence needs to be built into the camera to make the game easy to play? How will I handle displaying actions at widely separated points?
How do I map the actions of an athlete, or an entire team of athletes, to the controls available to the player? Will the functions of the buttons need to change during the course of play? When and why? What additional markings should I draw on the field of play to compensate for the player's lack of depth perception? What pop-up windows over the play will the player need, and how do I prevent those from obscuring the action? When play is not in progress, how does the rest of the user interface look and work?
What roles will the player play in the sport? Athlete, coach, general manager? When does the player switch from one to another and why?
What's the general structure of the game? What screens do I need, and how do they lead from one to another? Can the player trade athletes among teams in the middle of the season, for example?
What changes will I need to make to the physics of the sport to make it playable by ordinary mortals ?
What characteristics describe an athlete's abilities? How will they affect the way her behavior looks on the screen? Will some athletes have ratings peculiar to the positions they play?
What states can the game be in, even in times between active play? How does an athlete behave in each state? What are her goals in each state, and in team play, what is the collective goal of the team in each state? How does the individual athlete's behavior contribute to meeting the team's goal?
Am I going to offer automatic simulation of matches? How will that be done?
What will the audio commentary be like? What events will it cover?
How does instant replay work?