ball girl       
noun [ C ] (also ballgirl) uk/ˈbɔːl ˌɡɜːl/ us/ˈbɑːl ˌɡɝːl/
 女球童
a girl who picks up balls during a tennis, football or other sports game and gives them back to the players
  The player gave his racket to a ball girl, which delighted the crowd. 球员把他的球拍送给了一个女球童,让观众非常高兴。 
 On Friday nights, she's a ball girl for the school's football team.  周五晚上,她给学校橄榄球队当女球童。 
 - More examples
 - In skating, ice sweepers serve as the equivalent of ball girls and boys in tennis.
 - They met at a tennis tournament: he was a player; she was a ball girl.
 - In her third year as a ballgirl, she hopes to work one of Federer's matches for the first time this week.