Strikes back in fight (4)
I believe the answer is:
spar
'fight' is the definition.
(sparring is a kind of fighting)
'strikes back' is the wordplay.
'strikes' becomes 'raps' (rapping is a kind of striking).
'back' says the letters should be written backwards.
'raps' written backwards gives 'SPAR'.
'in' acts as a link.
(Other definitions for spar that I've seen before include "Raps with large beam" , "piece of wood?" , "Raps with large timber" , "Mineral; strong pole" , "Do up (bird for oven)" .)