In gameplay, a good stroke must touch the front wall above a 26.5 inches (67 cm) high wooden (often cloth-covered) board before touching the floor. The ball may touch the side walls before reaching the front wall. The player returning a good stroke may play the ball on the volley, or after one bounce on the floor. Gameplay is basically identical to squash, albeit without drop shots or lobs! The speed of the ball and tension of the racket strings used means that the play is fast, and potentially dangerous. Lets (replayed points) are common, as the striker should not play the ball if doing so risks hitting another player. Yet unlike in squash, strokes are not given if a player gets in the way such is the often exciting and frenetic gameplay. However, this danger is minimal, since the patient coaching all players receive engrain a solid tactical awareness in all participants. Matches are normally observed by a "marker" and a “referee”, who has the duty to call "Play" after each good stroke to denote that the ball is "up". Games are to 15 points, unless the game is tied at 13–all or 14–all, in which case the game can be "set" to 16 or 18 (in the case of 13–all) or to 15 or 17 (in the case of 14–all) at the option of the player first reaching 13 or 14. Only the server (hand-in) can score—the receiver (hand-out) who wins a rally becomes the server. Return of service can be extremely difficult, and, in North America, only one serve is allowed. At the top level of the game, aces (when a server beats their opponent without their opponent touching the ball) are somewhat rarer which results in physically draining rallies. Matches are typically best of five games, but earlier rounds of some tournaments can be best of 3 games - or even an adapted 'first to 30 points' game.