THE BALL CHANGE RULE.........

This depends on the federation that the event is played under. In tournaments played under the International Tennis Federation rules, balls are changed after the first 9 games, then after the next 11 games, then after the next 9 games, then after the next 11 games, and so on. In ATP and WTA tournaments, balls are changed after the first 7 games keeping in view the warmup at the beginning of the match and then every 9 games after that.