ball girl

Sports a girl who retrieves balls that have gone out of play, as in tennis and baseball, or a girl in charge of the extra balls used in practice, as in basketball and football

See ball girl in American Heritage Dictionary 4

noun
  1. A woman attendant on a tennis court who collects the ball when it is out of play.
  2. A girl who is in charge of the extra balls used in practice or those that are out of play, especially in baseball.
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