General
The ball is made of black rubber. It weighs 2.3 ounces and is 1 7/8 inches in diameter. Players usually wear gloves, but it isn't required.
In all forms of the sport, a player has an obligation to let the opponent play the ball. If the player gets in the opponent's way, or if the ball strikes the player, it is a "hinder." If the obstruction is judged accidental, the ball is dead and the point must be replayed. If it is an avoidable hinder, the penalty is loss of point or loss of service.
Four-Wall
The four-wall court is 40 feet long and 20 feet wide, and there is a front wall 20 feet high. The back wall is only 12 feet high. A "short line" crosses the court 20 feet from the front wall; 5 feet in front of this is the service line. An 18-inch strip on either side of the court, between these two lines, is called the service box. There is a vertical line on each side wall marking the receiving zone, 5 feet behind the short line.
The server drops the ball to the floor, between the short and service lines, and as it bounces up, strikes it so that it hits the front wall and lands on the floor behind the short line. (The ball can strike a side wall before hitting the floor.)
The receiver must stand in the receiving zone until the server strikes the ball. Only the serving side can score a point. After a legal serve, the sides take turns hitting the ball; it can hit any wall, and the ceiling, in any order, provided that it hits the front wall before it hits the floor. Play continues until one side fails to make a proper return. Game is 21 points.
In four-wall doubles, the server's partner must stand in one of the service boxes and the partner's back must be against the side wall until the serve has struck the floor.
Three-Wall
There are two versions of three-wall handball. The most common is played on a court without a back wall, and the rules are identical to those of the four-wall sport, except that a ball which carries over the back line on the fly is out, and results in either loss of a point or loss of service.
The other, played primarily in Greater New York, uses a court similar to that for jai alai, with a front wall, a back wall, and only one side wall.
One-Wall
The one-wall court is 34 feet long and 20 feet wide, and the one wall is 16 feet high. There is no ceiling. The short line is 16 feet from the front wall; the service line is a simple, 6-inch mark, 9 feet behind the short line. The rules are identical to those of the four-wall game except, of course, that there is only one wall to bounce the ball from.