American handball, known as handball in the United States and sometimes referred to as wallball, is a sport in which players use their hands to hit a small, rubber ball against a wall such that their opponent(s) cannot do the same without the ball touching the ground twice nor hitting out-of-bound. The three versions are four-wall, three-wall and one-wall. Each version can be played either by two players (singles), three players (cutthroat) or four players (doubles), but in official tournaments, singles and doubles are the only versions played.