Wallyball is volleyball played on a racquetball court. You can play off the walls and ceiling if you want. But diving for the ball without elbow and knee pads is not really recommended. The court floor doesn't give anywhere near as much as a sand volleyball court.
It is a great way to burn off some calories, which are replaced by hitting a restaurant after the games are over. The friends that I play wallyball with play for the fun of it.