Each player gets a ball and stands in a line facing a gym wall, so that each player is about 10 feet away from the wall.
At a signal, they each throw their ball against the wall, but have to catch a DIFFERENT ball than the one that they threw.
Behind them stand two catchers (you can start with the leaders being the catchers if you like), who try to get any of the balls.
Whoever has not caught a ball is out, and joins up with the catchers.
Eventually there is just one player who has a ball (or it is tied).
This game can get quite rambuncious at the end as the catchers are all trying to stop the final players from getting a ball.