Handball is a competitive game in which either hand or either fist may be used to serve and return the ball. The objective is to win each rally by serving or returning the ball so the opponent is unable to keep the ball in play. A rally is won when one player is unable to return the opponent's shot to the front wall before it touches the floor twice, or when a player returns the ball so that it hits the floor before striking the front wall. Four-wall handball may be played by two, three or four players. When played by two, it is called singles; when played by three, cutthroat, and when played by four, doubles. Points are scored only by the serving side when it serves an ace (un-returnable serve) or wins a rally. When the serving side loses one rally in singles or two rallies in doubles, it loses the serve. Losing the serve is called an "out". A match is won by the first side winning two games. The first two games of a match are played to 21 points. In the event each side wins a game, a tiebreaker is played to 11 points.