Rules

29. Role of Court Officials
In matches where an Umpire is appointed, his decision shall be final; but where a Referee is appointed, an appeal shall lie to him from the decision of an Umpire on a question of law, and in all such cases the decision of the Referee shall be final.

In matches where assistants to the Umpire are appointed (Linespersons, Net-cord Judges, Foot-fault Judges) their decisions shall be final on questions of fact except that if in the opinion of an Umpire a clear mistake has been made he shall have the right to change the decision of an assistant or order a let to be played. When such an assistant is unable to give a decision he shall indicate this immediately to the Umpire who shall give a Decision. When an Umpire is unable to give a decision on a question of fact he shall order a let to be played.

In Davis Cup matches or other team competitions where a Referee is on Court, any decision can be changed by the Referee, who may also instruct an Umpire to order a let to be played.
The Referee, in his discretion, may at any time postpone a match on account of darkness or the condition of the ground or the weather. In any case of postponement the previous score and previous occupancy of courts shall hold good, unless the Referee and the players unanimously agree otherwise.

USTA Comment: See fourth USTA Comment under Rule 30 regarding resumption of suspended match.

Case 1. The Umpire orders a let, but a player claims that the point should not be replayed. May the Referee be requested to give a decision?
Decision: Yes. A question of tennis law, that is, an issue relating to the application of specific facts, shall first be determined by the Umpire. However, if the Umpire is uncertain or if a player appeals from his determination, then the Referee shall be requested to give a decision, and his decision is final.

Case 2. A ball is called out, but a player claims that the ball was good. May the Referee give a ruling?
Decision: No. This is a question of fact, that is an issue relating to what actually occurred during a specific incident, and the decision of the on-court officials is therefore final.

Case 3. May an Umpire overrule a Linesman at the end of a rally if, in his opinion, a clear mistake has been made during the course of a rally?
Decision: No. An Umpire may overrule a Linesman only if he does so immediately after the mistake has been made.

USTA Comment: See Rule 17, Case 1 regarding non-officiated matches.

Case 4. A Linesman calls a ball out. The Umpire was unable to see clearly, although he thought the ball was in. May he overrule the Linesman?
Decision: No. An Umpire may only overrule if he considers that a call was incorrect beyond all reasonable doubt. He may only overrule a ball determined good by a Linesman only if he has been able to see a space between the ball and the line; and he may only overrule a ball determined out, or a fault, by a Linesman only if he has seen the ball hit the line, or fall inside the line.

Case 5. May a Linesman change his call after the Umpire has given the score?
Decision: Yes. If a Linesman realizes he has made an error, he may make a correction provided he does so immediately.

Case 6. A player claims his return shot was good after a Linesman called "out." May the Umpire overrule the Linesman?
Decision: No. An Umpire may never overrule as a result of a protest or an appeal by a player.