assistant referee
US /əˌsɪs.tənt ˈref.ə.ri/
UK /əˌsɪs.tənt ˈref.ə.ri/

1.
помощник судьи, лайнсмен
an official who assists the referee in a soccer match, typically by indicating when the ball is out of play or when a player is offside
:
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The assistant referee raised the flag for offside.
Помощник судьи поднял флажок, сигнализируя об офсайде.
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The decision was confirmed by the assistant referee.
Решение было подтверждено помощником судьи.