fight boner

Getting hyped and excited about a fight going on around or being in a fight and enjoying it.

the latter possibility arises if you like having the adversary as adversary, for various reasons

Hisoka, an experienced fighter in a tournament arena setting has been watching a newbie gon develop at amazing rate and they finally face off. Mid fight, Hisoka to Gon:
Oh.. Don't look at me like that. I'm getting turned on!!! (fight boner)