A bird box dispute (7)
I believe the answer is:
sparrow
'a bird' is the definition.
(sparrow is a kind of bird)
'box dispute' is the wordplay.
'box' becomes 'spar' (sparring is a kind of boxing).
'dispute' becomes 'row' (I've seen this before).
'spar'+'row'='SPARROW'
(Other definitions for sparrow that I've seen before include "Passerine bird" , "one on the wing" , "Little brown bird" , "Common town bird" , "Small brown bird" .)