Revolutionary nut's reign over (9)
I believe the answer is:
insurgent
'revolutionary' is the definition.
(I've seen this before)
'nut's reign over' is the wordplay.
'over' indicates anagramming the letters.
'nuts'+'reign'='nutsreign'
'nutsreign' is an anagram of 'INSURGENT'.
(Other definitions for insurgent that I've seen before include "rising" , "freedom fighter" , "Unresting like a rebel" , "Revolting" , "Rebel, revolutionary" .)