A friend you are, I say, and not playing for money (7)
I believe the answer is:
amateur
'i say and not playing for money' is the definition.
I can't judge whether this defines the answer.
'a friend you are' is the wordplay.
'friend' becomes 'mate' (mate is a kind of friend).
'you are' becomes 'ur' (text or internet abbreviation).
'a'+'mate'+'ur'='AMATEUR'
Can you help me to learn more?
(Other definitions for amateur that I've seen before include "Unpaid (sport)" , "Of sportsman, not professional" , "unskilful" , "One who pursues an activity as a pastime only" , "lacking professionalism" .)