Prize for a revolting sketch (5)
I believe the answer is:
award
'prize' is the definition.
(synonyms)
'a revolting sketch' is the wordplay.
'revolting' says the letters should be written backwards.
'sketch' becomes 'draw' (I've seen this before).
'draw' back-to-front is 'ward'.
'a'+'ward'='AWARD'
'for' acts as a link.
(Other definitions for award that I've seen before include "Write up" , "Present - prize" , "Adjudge" , "Official prize in a draw" , "Give, as an honour" .)