Not professional (7)
I believe the answer is:
amateur
'not professional' is the definition.
('amateur' is the opposite to 'professional')
This is all the clue.
(Other definitions for amateur that I've seen before include "One who pursues an activity as a pastime only" , "lacking professional expertise" , "he won't get paid" , "A non-professional sportsman" , "Inept, non-professional" .)