Four square requires only a ball and a court made of four squares. With such little required equipment, almost no setup, and short rounds of play that can be ended at any time, it is a popular playground game. Gameplay varies significantly from region to region.
The objective in four square is for individual players to enter the court in the lowest square and move up by eliminating players in higher squares.  Once at the top square the player begins to score points, and has the privilege of serving the ball to start each round. Players are eliminated when they cause any number of specific errors. With each elimination, players advance to until the lowest square is available and a new player joins the court in that position. Any number of players may wait in a line outside the court for their turn to play.
Four square is played on a square court divided into four smaller squares of equal size. Different communities or groups use different size courts, ranging from 16 to 24 feet . Court sizes are often adjusted to be appropriate for age or skill level.
The outermost lines of the court are considered fair play and the ball may land on any portion of an outside line and still be in play. The inside lines are designated as out of bounds and balls landing on any portion of an inside line are in error. A popular abbreviation of these rules is known as 'inside out, outside in'. Balls landing outside the court are considered errors as well. 
Starting gameplay and service
Each round of the game begins with the player in the top square serving the ball. The server must first drop the ball in their square then serve to another square. The serve is intended to put the ball into play fairly and must be reasonably returnable by the first receiving player. From this point on, regular game play follows until a player is eliminated. You may spike the ball through out the game and not be out.
Players must allow the ball to land once in a square, and the occupant of that square must return the ball to any other player's square by hitting or striking the ball with their hands. They may hit with one or both hands but must hit cleanly with no holding, fumbling or catching; or be eliminated. Once the ball lands in a new player's square, that player must return it, and so forth, until a player makes an error and is eliminated.
Errors and elimination
Players may be eliminated for the following errors:
A player hits the ball out of bounds.
A player allows the ball to bounce more than once in their square.
A player fails to hit the ball properly into another player's square.
A player hits the ball more than once before returning it to another square.
A player violates a special rule. Four square is known for its many spontaneous rules.
Eliminated players leave the court, all remaining players move up to the next highest square, and a new player joins in the lowest square.
Officiation and judging
Four square is a fast game and often played by younger children. It is often difficult for children to self-govern a game of four square and it is important to create some form of officiation or judging when appropriate.