play a game/play the game

play a game 是指“玩游戏”，play the game 是指“讲信义”“做事光明正大”“按规矩办事”“按规矩比赛”。例如：

1. I think he will play the game and return your book. (ELD) 我认为他会守信用, 把书还给你的。

2. He is an honest man and has always played the game. (LDCE) 他是个诚实的人,一向守信用。