In professional tennis, the players are issued a new set of tennis balls after the first seven games, and every nine games thereafter. (The players warm up with the first set of balls, so they are removed after seven games.)
Here is Maria Sharapova striking a backhand during a match at the BNP Paribas Open in Indian Wells.

Take a closer look. You can see the tennis ball is crushed! The strings are deformed past the racket frame, and thus the flattened ball is visible both behind and in front of the racket frame. It in no way resembles the fuzzy sphere prior to impact!
