Play with any kind of ball that bounces well but the standard is a red playground ball.
In the standard game, there are four squares painted on the ground, all touching each other, making one, larger square. The larger square is roughly 8' x 8' or sometimes 6' by 6' and the squares should be numbered 1-4. Each player occupies one of the squares. The squares each have a rank order. The square with the highest rank is called the 'King' (sometimes the 'Ace'). The other squares sometimes have names, and sometime don't or simply go by the numbers. The #2 square may be called the 'Prime Minister', or the other three may be called the 'Queen', 'Prince', and 'Princess'. The person standing in the highest number square or the 'king square' always serves. He or she can serve to any of the other squares on the first attempt, but this choice becomes limited if the serve is not successful. In a successful serve, the server drops the ball in his or her own square, lets it bounce once, and then hits it into another square. The person standing in that square lets the ball bounce in their square, before hitting it underhanded to any other square.
After a successful serve, play continues with volleying from one square to another. If a player fails to volley legally, he or she is out. In a legal volley, the ball bounces once and only once in a player's square then continues on to an opponent's square. The player can hit the ball before it bounces in his or her square to gain control of it. Whether or not the person hits the ball before it bounces, he or she must hit the ball once after it bounces. Any instantaneous touch of the ball is considered a hit.
Any player who commits a foul is out. Several types of fouls can occur during play. A bobble occurs when a player hits the ball more than once between bounces. If a player touches the ball only once but his or her hand remains in contact with the ball longer than the instantaneous time of a hit, the player is said to have carried the ball. Touching the ball with two hands, unless both hands hit simultaneously, is considered holding. Any hit that causes the ball to bounce up higher than the head of the receiver is a slam. If a player who is suppose to hit a ball does not and the ball bounces twice, they are out.
If the ball bounces out of bounds (out of the court), or on a boundary line, the last person to touch it is out. The ball may, however, legally fly outside the bounds of the court and be returned to play as long as it does not bounce on the ground outside the court. Note that a ball may bounce off a wall or other object that is on or near a boundary and be legally volleyed as long as its next bounce is in another player's square. A player who hits the ball so that it bounces on any of the lines that mark the boundaries between squares is out.
When a player gets out, the person loses his or her position on the court. If there are no more players than there are spaces, the person who is out moves to the #1 or princess square. If there are more players than squares, the person who is out gets in line. The first and second players waiting in line become judges. Players in squares numbered lower than this person's original square advance to the next higher number square.
Judging is an active part of the game of four-square. If there are more players than squares, the players who are not volleying serve as judges. These players station themselves along the boundary lines between squares. Each judge is responsible for calling fouls and settling questions about on which side of his or her line the ball bounced. The player next in line to occupy square #1 is the chief judge. This person settles disputes. If the chief judge desires, he or she can call a do-over, in which case the entire point is played over again from the serve. The decisions of the judges are final. Though they do err on occasion, good sportsmanship dictates that every player accept his or her share of erroneous calls. If there are no players to serve as judges, the players judge among themselves. When a dispute arises, the point is declared a do-over.
The game continues until the ball is hit out of bounds or a player can not retrieve the ball. If the player in square number one loses, each of the players move up one square and a new number one comes into play. Player number one moves to square four.