Bludgeon zealots in revolution (4)
I believe the answer is:
stun
'bludgeon' is the definition.
(bludgeon can mean to shock or stun)
'zealots in revolution' is the wordplay.
'zealots' becomes 'nuts' (nut can mean a zealot or enthusiast).
'in revolution' is a reversal indicator (letters revolve back).
'nuts' reversed gives 'STUN'.
(Other definitions for stun that I've seen before include "Render unconscious" , "Daze or bewilder" , "Make dazed or numb" , "Nuts (anag)" , "cause amazement" .)