Tennis is a sport that is either played individually or in pairs. The object of the game is to play the ball so that the opponent is unable to play a return.
The International Tennis Federation (ITF) is the governing body of the game of tennis and its duties and responsibilities include determination of the Rules of Tennis. The United States Tennis Association (USTA) comments have the same weight and force in USTA tournaments as do ITF Cases and Decisions. The USTA Friend at Court: The USTA Handbook of Tennis Rules and Regulations rules that the type of ball and the ball change pattern must be consistent within a tournament.
F. Balls and Ball Change Pattern
1. The type of ball. At the sectional championship level and above the type of ball shall be consistent throughout a tournament event unless the playing surface or conditions are changed. For example, both heavy duty felt balls and regular felt balls normally shall not be used in the same tournament event. Compliance is recommended for tournaments below the sectional championship level.
2. Approved balls. In all USTA tournaments and leagues, the ball used must be on the list of balls approved by the USTA or must be otherwise authorized by the USTA. The USTA shall rule on whether any ball or prototype complies with the specifications adopted by the ITF pursuant to the ITF Rules of Tennis or is otherwise authorized for play. Rulings may be taken on the USTA’s own initiative or upon application by any party with a bona-fide interest, including any player, equipment manufacturer, ITF, Sectional Association, District Association, or Organization Member. Rulings shall be made in accordance with the then current testing procedures adopted by the USTA. A list of balls approved by the USTA shall be published.
FAC Comment I.F-1: A current list of the USTA approved balls is available at www.usta.com.
3. Referee determines ball change pattern. The Referee shall determine the ball change pattern subject to the right of the Chair Umpire to order a ball change at other than the normal time when the Chair Umpire determines that abnormal conditions warrant so doing.
4. Number of balls. New balls shall be used to start a match commencing with the warm-up. At least three balls are recommended for use at matches at the sectional championship level. At least three balls shall be used for matches at tournaments above the sectional championship level. When a tournament specifies new balls for a third set, new balls shall be used unless all players agree otherwise.
5. Warm-ups. Warm-ups in which the match balls are used are treated as the equivalent of two games of match play.
United States Tennis Association – www.usta.com
Friend at Court: The USTA Handbook of Tennis Rules and Regulations: assets.usta.com/assets/1/15/2013_Friend_At_Court1.PDF
Photo – viterbivoices.usc.edu/tag/society-of-women-engineers/page/6/