Scroll in Play works in a similar way as the Catch mode, but instead of having the SPL play across the Arrange area's Regions, the Arrange area's Regions scroll past a stationary SPL.
From the Arrange window's local menu bar, choose View > Scroll in Play.
Play from the beginning of the song. The SPL plays to the middle of the Arrange window, at which point it stops and the Arrange area's Regions start scrolling left past the SPL.
To turn Scroll in Play off, choose View > Scroll in Play once again.