game face
noun [ C ] informal uk/ˈɡeɪm ˌfeɪs/ us/ˈɡeɪm ˌfeɪs/
比赛脸（指严肃、坚定的表情）
a serious or determined expression that you put on when you are going to try to win or achieve something
Most players had their game face on and just ignored the calls from the crowd. 大多数球员都是一副比赛脸，对观众的呼喊置之不理。