Hits back in fight (4)
I believe the answer is:
spar
'fight' is the definition.
(I know this)
'hits back' is the wordplay.
'hits' becomes 'raps' (I've seen this in another clue).
'back' says the letters should be written in reverse.
'raps' in reverse letter order is 'SPAR'.
'in' acts as a link.
(Other definitions for spar that I've seen before include "Do up (bird for oven)" , "Fight - something probably rigged?" , "A mineral; nautical pole" , "Length of wood" , "Crystalline mineral" .)