Intellectual is supporter in fight (8)
I believe the answer is:
brainbox
'intellectual' is the definition.
'supporter in fight' is the wordplay.
'supporter' becomes 'bra' (I've seen this before).
'fight' becomes 'box' (boxing is a kind of fighting).
'bra'+'in'+'box'='BRAINBOX'
'is' is the link.
(Other definitions for brainbox that I've seen before include "quiz champion?" , "Skull - clever clogs" , "Einstein?" , "Mastermind" , "Clever type" .)