Criticise musical style with standard backing (3)
I believe the answer is:
rap
'criticise musical style' is the definition.
'rap' can be an answer for 'criticise' (I've seen this in another clue). I'm unsure of the 'musical style' bit.
'standard backing' is the wordplay.
'standard' becomes 'par' (standard of play in golf).
'backing' says the letters should be written backwards.
'par' written backwards gives 'RAP'.
'with' acts as a link.
(Other definitions for rap that I've seen before include "talking during musical performance" , "Knock for par" , "Type of popular music" , "Knock loudly" , "Blame, punishment" .)