Boxer, perhaps, went up for flower (3,4)
I believe the answer is:
dog rose
'flower' is the definition.
(I have seen 'Hedgerow flower ' mean 'dog rose' so perhaps 'flower' could also mean 'dog rose')
'boxer perhaps went up' is the wordplay.
'boxer perhaps' becomes 'dog' (boxer is a kind of dog).
'went up' becomes 'rose' (I've seen this in another clue).
'dog'+'rose'='DOG-ROSE'
'for' is the link.
(Other definitions for dog rose that I've seen before include "wild shrub" , "Flower of the hedgerow" , "Hedgerow plant" , "bloomer" , "something smelling nice in the hedgerow" .)