Throw in the towel 举白旗
It means to quit.This phrase comes from boxing.When a boxer is too beat up to continue,his coach throws a towel into the ring to signal that the fight is over.
Note:
Throw in the towel的意思是认输,来源于拳击比赛.当拳击手打不过对方,他的教练会抛一条毛巾入场,表示认输.
例：The company threw in the towel after losing all of its major customers.
公司丢了所有的主要客户之后只好举白旗认输了.