Dispute on chairs around piano (4)
I believe the answer is:
spat
'dispute' is the definition.
(I know that spat is a type of dispute)
'on chairs around piano' is the wordplay.
'on chairs' becomes 'sat' (sat on chairs).
'around' means one lot of letters goes inside another.
'piano' becomes 'p' (musical abbreviation).
'sat' going around 'p' is 'SPAT'.
(Other definitions for spat that I've seen before include "Pat's involved in petty quarrel" , "A small tiff or quarrel" , "Spoke violently" , "Observed" , "Minor argument" .)