My informant used to play a variant of Wallball at his Bay Area elementary school called “Butts Up.”  Like with regular Wallball, the game was played against the wall of a building or room, with one ball and many participants.  Players had to throw the ball against the wall without the ball first bouncing off the ground.  If the ball touches a player and then touches the floor, that player must run to the wall before the next time someone performs a successful wall bounce (player -> wall without touching floor).  If a player makes it to the wall in time, he or she is safe and may resume play.  If the ball makes it there first, that player receives a point.  Additionally, a player may attempt to perform a fast catch, whereby the player catchs the ball immediately after it has bounced off the wall, before it touches the floor again.  If the player successfully performs a fast catch, then the player who threw the ball gets a point.

My informant’s version of the game uses letters instead of points.  Each point spells out the word B-U-T-T-S and when a player has gotten all 5 letters, they must stand against the wall with their butt in the air while every other player gets a chance to peg them in the ass with balls.  Additionally, instead of a rubber playground ball, Butts Up was played exclusively with a tennis ball, and players were allowed to catch the ball in between throws, instead of just fast catches.  Also after a player has been ass-pegged for spelling BUTTS, instead of being out, the player simply returns to the game with a clean slate, albeit a sore ass.  Another one of my informants also said that some kids from his elementary school, back in New York, played this version of Wallball, and even called it by the same name of “Butts Up.”  According to him, this version of the game was reserved for the hardest of hardcore children.