Fist fight (5-2)
I believe the answer is:
punch-up
'fist fight' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for punch-up that I've seen before include "Brawl (colloq.)" , "Fisticuffs incident" , "An informal brawl, a fight with fists" , "An informal fist-fight or brawl - strike vertically?" , "Street brawl" .)