Paddleball was created at the University of Michigan in 1930 by Earl Riskey, a Physical Education instructor in that university. It is played in one of two versions: 1-wall paddleball and 4-wall (indoor) paddleball. The latter is similar to a racquetball court. Game is played with a rimless paddle and a ball slightly smaller than a tennis ball. Paddleball may by played by two players (singles) or four players (doubles). The object is to win the rally by serving or returning the ball so the opponent is unable to return the ball to the front wall before it touches the floor twice. Points are scored only by the serving side when it serves an ace or wins a rally. Match is won by the side that wins two of a possible 3 games by scoring 21 points first (lesser points for a win are also common). If the games are tied 1-1, the tie-breaker game is won by the side that scores 11 points first.