Lyric discussion by kill3rm0nkey 

Cover art for Boxer lyrics by Gaslight Anthem, The

First time I heard this song I thought it was about someone who used to be this strong figure who took all his beatings standing up, but as time has gone on he can't deal with everything the way he used to. I think the line "remember when I knew a boxer" is the singer looking at the person and remembering when they were this kind of fighter or warrior.