An unorganized boxing match that usually happens on the streets or in a schoolyard. A fist fight is strictly throwing punches, unlike most street fights. If the participants start grappling and whatnot, then it is more of a brawl.
The teacher and student started fist fighting, but it eventually turned into a brawl.
to furiously masturbate
That is so lonely, I heard he spent all weekend fist fighting with himself.