The United States Tennis Association (USTA) states that a player can be defaulted if he has committed a rule violation. A default can occur before or during a match for a variety of reasons. Flagrant violations always result in a default, while other violations may be awarded penalties per the judgment of the referee. A walkover is when a player is unable to play his scheduled match and withdraws from the tournament. Usually the player has a legitimate excuse. In either case, the opponent is awarded the win.
Violent behavior by a tennis player is not tolerated during a tournament. If a player injures his opponent by throwing his racket or by hitting the ball, he is immediately defaulted. Other reasons for an immediate default include, but are not limited to, physical attacks against another player, tournament official or spectator. According to the Friend at Court handbook, unsportsmanlike acts such as spitting on a person, making religious, racial or sexual orientation slurs will result in an immediate default of the player.
Betting on a tournament match is not allowed. A player who violates this rule is immediately defaulted by the tournament referee. This player may also be banned from any future connection with the tournament.
Lateness or No-Show Defaults
If a court is available for match play and a player has not checked in within 15 minutes of the scheduled time, he will be penalized or defaulted. Depending on the number of minutes the player is late, the penalties include the loss of the toss -- this determines who serves first, and in the loss of up to three games. If the player checks in after 15 minutes or does not show at all, he is defaulted.
Code Violation Defaults
A code violation is when a player breaks a tennis rule or regulation during a tournament. The USTA set up a point penalty system to control code violations, unsportsmanlike behavior and help maintain fair play. Examples of code violations are deliberately breaking your racket, audible profanity, refusing to follow a tournament official's instructions and intentionally delaying the game. Usually, when a player commits a code violation, the tournament official gives him a warning. If the same violation happens again, the player is penalized one point. With the next offense the player is penalized one game. The player is defaulted the next time the violation takes place.
Walkovers typically take place before a match starts. If a player withdraws from a tournament prior to his first match due to an injury, illness or a personal reason, the opponent is awarded a walkover, is credited with a win and advances on to the next round of the tournament. A player who refuses to play for any other reason is defaulted.
On occasion tournament administrators make mistakes which can lead to a walkover situation. Giving a player the wrong start time for his match is an example of an administrative error.