The basic rules of Singles Squash
(Updated to show the new scoring introduced 1st April, 2009)

The Game

The game of squash is a racket game and is played on an indoor-enclosed rectangular court.  

A match shall consist of the best of five games. Each game is to eleven points, except when the score is ten-all, then there shall be a tie breaker played until there are two clear points. 

Points

Points are scored by either player. When the server wins a stroke, the server scores a point; when the server loses a rally the receiver wins the point.

The right to serve first is decided by the spin of a racket. Thereafter, the server continues to serve until losing a stroke, where upon the opponent becomes the server, and this procedure continues throughout the match. At the beginning of each game and each handout, the server has the choice of serving from either box and thereafter shall serve from alternate boxes while remaining on the serve. For a service to be good it shall be served directly on to the front wall between the cut-line and the out line so that on its return, unless volleyed, it reaches the floor within the quarter of the court opposite to the server's box. A service is good when it doesn't result in hand-out. The service becomes hand-out and the server loses the stroke if:

• The ball, after being dropped or thrown for service, touches the wall(s), floor, ceiling or any object(s) suspended from the walls or ceiling before being served. - Called "Fault".
• At the time of striking the ball the server fails to have part of one foot in contact with the floor within the service box, without any part of that foot touching the service box line (part of that foot may project over this line provided that it does not touch the line). - Called "Foot fault".
• The ball is served out, - Called "Out".
• The ball is served against any part of the court before the front wall. - Called "Fault".
• The ball is served on or below the cut line. - Called "Fault" if above the board and "Down" if on or below the board. The first bounce of the ball, unless volleyed by the receiver, is on the floor or outside the short or half court lines of the quarter court opposite to the server's box. - Called "Fault".
• The ball, after being served, and before it has bounced on the floor more than once and before it has been struck by the receiver, touches the server or anything the server wears or carries. - Called "Down".

After a good service has been delivered, the players return the ball alternately until one fails to make a good return.

A return is good if the ball, before it has bounced more than once, is returned correctly by the striker on to the front wall above the board, without first touching the floor or any part of the striker's body or clothing, or the opponent's racket, body or clothing, provided the ball is not hit out. It shall not be considered a good return if the ball touches the board before or after it hits the front wall and before it bounces on the floor.

If the ball, before reaching the front wall, hits the striker's opponent or racket, or anything they wear or carry, the ball shall cease to be in play and the striker shall win the stroke if the return would have been good and the ball would have struck the front wall without first touching any other wall. If the return would have been good but the striker has either followed the ball round and turned or allowed it to pass around themselves - in either case by striking the ball to the right of the striker's body after the ball had passed to the left (or vice versa) then a let shall be allowed in all cases. If the ball either has struck, or would have struck, any other wall, and the return would have been good, a let shall be allowed unless, in the opinion of the referee, a winning return has been intercepted, in which case the striker shall win the stroke. If the return would not have been good, the striker shall lose the stroke.

When it is their turn to play the ball, a player is entitled to freedom from interference by their opponent. To avoid interference, the opponent must make every effort to provide the player with unobstructed direct access to the ball, a fair view of the ball, freedom to hit the ball and freedom to play the ball directly to the front wall. Interference occurs if the opponent fails to fulfill any of the above, irrespective of whether they make every effort to do so.

If the striker strikes at, and misses, the ball he may make further attempts to strike it. If, after being missed, the ball touches an opponent or his racket, or anything he wears or carries, then, if, in the opinion of the Referee: 

• The striker could otherwise have made a good return, a let shall be allowed, 
• or the striker could not have made a good return, his side shall lose the stroke.
• If any such further attempt is successful, resulting in a good return being prevented from reaching the front wall by hitting one of the striking side's opponent or anything he wears or carries, a let shall be allowed in all circumstances. 
• If any such further attempt would not have resulted in a good return, the striking side shall lose the stroke.  

Lets

A let is an undecided rally. The rally, in respect of which a let is allowed, shall not count and the server shall serve again from the same box. In addition to lets allowed under other rules, lets may, or shall, be allowed in certain other cases. 

• If, owing to the position of the striker, the opponent is unable to avoid being touched by the ball before the return is made. 
• If the ball in play touches any article lying on the floor 
• If the striker refrains from hitting the ball owing to a reasonable fear of injuring their opponent. 
• If, in the opinion of the Referee, either player is distracted by an occurrence on or off the court, 
• If the receiver is not ready and does not attempt to return the service. 
• If the ball breaks during play. 
• If the Referee is asked to decide an appeal and is unable to do so. 

Where a player is struck by the ball, the Referee shall decide, without appeal, whether a let is to be allowed or the stroke awarded to the striker.

At any time, when the ball is not in actual play, another ball may be substituted by the mutual consent of the players, or by an appeal by either player at the discretion of the Referee.

Immediately preceding the start of play the two players shall be allowed on the court of play together for a period of five minutes for the purpose of warming up the ball to be used during the match. After two and a half minutes of warm up, the Referee shall call "Half Time" and ensure that the players change sides, unless they mutually agree otherwise. The Referee shall also advise when the warm up period is complete with the call of "Time". An interval of up to ninety seconds shall be permitted between the end of the warm up and start of play.