Bird in box leading to argument (7)
I believe the answer is:
sparrow
'bird' is the definition.
(sparrow is a kind of bird)
'box leading to argument' is the wordplay.
'box' becomes 'spar' (sparring is a kind of boxing).
'leading to' means one lot of letters go next to another (some letters go before or lead others).
'argument' becomes 'row' (to row is to argue).
'spar'+'row'='SPARROW'
'in' acts as a link.
(Other definitions for sparrow that I've seen before include "Common town bird" , "Small brownish bird" , "Singing bird" , "fowl, using outdated term" , "(Formerly very) common British bird" .)