Champion's card sure to be corrected (8)
I believe the answer is:
crusader
'champion's' is the definition.
(I've seen this before)
'card sure to be corrected' is the wordplay.
'to be corrected' indicates an anagram.
'card'+'sure'='cardsure'
'cardsure' is an anagram of 'CRUSADER'.
(Other definitions for crusader that I've seen before include "RA cursed (anag) - one fighting for a cause" , "Vigorous campaigner" , "Person engaged upon a cause" , "Richard I, for instance" , "Advocate for a cause - rude scar (anag)" .)