Stalin as a crazy aggressor (9)
I believe the answer is:
assailant
'aggressor' is the definition.
(I've seen this before)
'stalin as a crazy' is the wordplay.
'crazy' is an anagram indicator.
'stalin'+'as'+'a'='stalinasa'
'stalinasa' is an anagram of 'ASSAILANT'.
(Other definitions for assailant that I've seen before include "An attacker like mugger" , "One attacking another" , "Aggressive sort" , "Aggressor" , "who is on the offensive?" .)