Friend mean to protect right with standard rent rising (8,7)
I believe the answer is:
sparring partner
'friend' is the definition.
(I have seen 'Argumentative friend' mean 'sparring partner' so perhaps 'friend' could also mean 'sparring partner')
'to protect right with standard rent rising' is the wordplay.
'to protect right with' becomes 'sparring' (I can't explain this - if you can you should believe this answer much more).
'standard' becomes 'par' (standard of play in golf).
'rising' is a reversal indicator (going up in a down clue).
'rent' written backwards gives 'tner'.
'sparring'+'par'+'tner'='SPARRING PARTNER'
'mean' acts as a link.
Can you help me to learn more?
(Other definitions for sparring partner that I've seen before include "Argumentative friend" , "disputatious associate" , "What a boxer needs" , "Boxer's opponent during training" , "hits rehearsed with me?" .)