Four square addendums:

In general, the ball cannot be "held", for much time. It can be caught but must move after about five seconds.

The square grid usually looks like this, and players rotate counter-clockwise from pawn to king. Players waiting to go "in" stand on the X.

|pawn |   KING    |
|  jack  | queen    |

 A player is usually "out" if the ball bounces twice (or three times, at the discretion of the group) within a player's square, or if an opponent throws the ball so it lands in the player's square but they cannot reach it to return it. You can get yourself out by throwing out of bounds.

"Moves" or "plays" are popular in four square. Some are a one-time move, others are chains.  You have to call moves--so basically if you do anything but just throw the ball normally, you have to yell it out. If you call a move, but mess it up, YOU are "out"--even if the person you threw it to didn't return the ball.

Ace: ball slammed in far corner of square, kind of a underhand sideswipe
toilet paper: thrower holds the ball against his or her chest, under chin, on the flat part of both arms, and rolls it down arms and off hands. The 'unrolling' move is where the name is from.
giant: throw the ball REALLY hard so it bounces over the other player's head.
typewriter: the ball is dribbled repeatedly in your opponent's square, maxing them out on bounces. Really easy to fumble!

popcorn: throw the ball to anyone. They must catch it, toss it in the air, and clap their hands once and yell "one" before catching the ball again, then throw the ball on. The next player has to clap and count "two", and so on.around the world: the ball must be thrown to the adjacent player, and continue around the square. This MUST continue in a circle until someone breaks it.death/deathmatch: the caller throws the ball to any player. These two must continue back and forth, not passing the ball to any other players, until one is eliminated