Hit poor piano (4)
I believe the answer is:
bump
'hit' is the definition.
(synonyms)
'poor piano' is the wordplay.
'poor' becomes 'bum' (both can mean poor quality).
'piano' becomes 'p'.
'bum'+'p'='BUMP'
(Other definitions for bump that I've seen before include "Slang for kill - . . . . off" , "Evidence of pregnancy - knock (into)" , "Lump caused by a blow" , "Speed restriction" , "Swelling caused by a blow perhaps" .)