Bird box on bank (7)
I believe the answer is:
sparrow
'bird' is the definition.
(sparrow is a kind of bird)
'box on bank' is the wordplay.
'box' becomes 'spar' (sparring is a kind of boxing).
'on' says to put letters next to each other.
'bank' becomes 'row' (I've seen this in other clues).
'spar'+'row'='SPARROW'
(Other definitions for sparrow that I've seen before include "Common small bird" , "Cock Robin's assassin" , "Finch-like bird" , "Common town bird" , "Winger" .)