Trade blows in Ring over strikes (4)
I believe the answer is:
spar
'trade blows in ring' is the definition.
(boxing ring)
'over strikes' is the wordplay.
'over' is a reversal indicator.
'strikes' becomes 'raps' (rapping is a kind of striking).
'raps' reversed gives 'SPAR'.
(Other definitions for spar that I've seen before include "Scrap" , "Mineral; plane's wing beam" , "Box (gently) - fight (verbally)" , "Shadow box" , "Raps with strong pole" .)