Blaze held back by sheriff (4)
I believe the answer is:
fire
'blaze' is the definition.
(I know that blaze is a kind of blast)
'held back by sheriff' is the wordplay.
'back by' is a reversal indicator.
'held' says the answer is hidden in the clue.
'erif' is hidden in the letters of 'sheriff'.
'erif' reversed gives 'FIRE'.
(Other definitions for fire that I've seen before include "See 5" , "Weaponry" , "Flame - dismiss - shoot" , "Blaze - sack" , "Trigger" .)