multiball system
noun [ S ] uk/mʌl.tiˈbɔːl ˌsɪs.təm/ us/mʌl.tiˈbɑːl ˌsɪs.təm/
（足球比赛中准备好多个球，在比赛用球出界时可随时替换的）多球系统
the practice of having a lot of balls available to use during a football game, any of which quickly replace the ball that is being used when it goes outside the playing area during the game