Cult rip off perpetrator (7)
I believe the answer is:
culprit
'perpetrator' is the definition.
(I know that perpetrator can be written as culprit)
'cult rip off' is the wordplay.
'off' indicates anagramming the letters.
'cult'+'rip'='cultrip'
'cultrip' is an anagram of 'CULPRIT'.
(Other definitions for culprit that I've seen before include "Person responsible for wrongdoing" , "baddie" , "he should have conviction" , "The one responsible for a crime" , "one awaiting trial" .)