The phrase "puts up a fight" refers to the act of resisting or opposing someone or something. Antonyms for this phrase could include "surrender," "yield," or "concede." Other options might be "comply," "cooperate," or "acquiesce." These words indicate a willingness to give in or go along with something, rather than pushing back or standing firm. While there may be occasions when it is appropriate to throw one's weight behind a cause or defend oneself against an attack, there are also times when it's better to be flexible and let things unfold without resistance.