Small bird box dispute (7)
I believe the answer is:
sparrow
'small bird' is the definition.
(type of bird)
'box dispute' is the wordplay.
'box' becomes 'spar' (sparring is a kind of boxing).
'dispute' becomes 'row' (row is a kind of dispute).
'spar'+'row'='SPARROW'
(Other definitions for sparrow that I've seen before include "House bird" , "A small chirpy city bird 97)" , "Small brownish bird" , "Common small bird" , "Robin's slayer" .)