Punching above your weight is one I always hear being used a lot also rope-a-dope is one I've heard used in news reports about stratergies in military conflicts to - which kind of leaves a bit of a bitter taste in my mouth - I always think of that being said with Ali's tongue in cheek charm - I don't really want to hear being stolen and used in discussion about horrible and illegitimate wars which result in death and suffering
(Sir) David Frost was screwed out of that phrase, he invented it, listen to the interview, post fight...
Roll with the punches has been said, and I think this the most used one. It is my favorite one as well.
square off : To assume a fighting stance; prepare to fight. chinless : a person, esp. an upper-class one, lacking strength of character