Racquetball is a racquet sport played with a hollow rubber ball in an indoor or outdoor court. Earl Riskey developed paddleball in the 1920's. Joe Sobek is credited with inventing the sport afterward in 1950, adding a stringed racquet to the game to increase velocity and control. Unlike most racquet sports, such as tennis or badminton, the court's walls, floor, and ceiling are legal playing surfaces, rather than out-of-bounds.

Normally, a racquetball game is played between two opposing players, though three- and four-player variations exist. Two-player games are called singles or "one-up" (1-on-1 for the entire game); three-player games are called "Ironman" or "Cut-throat" (2-on-1 for the entire game) wherein each player take turns serving to the other two; the "California" variation is a 3-player game wherein it is played as a three-way singles game, except that the player losing the point remains in the back court while the other two play the next point; the four-player game is called "doubles" and played as teams.