Courage of supporter to a great degree (7)
I believe the answer is:
bravery
'courage' is the definition.
(I know that courage can be written as bravery)
'supporter to a great degree' is the wordplay.
'supporter' becomes 'bra' (a bra gives support to breasts).
'to a great degree' becomes 'very'.
'bra'+'very'='BRAVERY'
'of' acts as a link.
(Other definitions for bravery that I've seen before include "bottle?" , "Heroism" , "heroic behaviour" , "Valour" , "Courage" .)