Sudden vivid memory of, say, Gordon Champion (9)
I believe the answer is:
flashback
'sudden vivid memory' is the definition.
'say gordon champion' is the wordplay.
'say gordon' becomes 'flash' (Flash Gordon).
'champion' becomes 'back' (I've seen this in other clues).
'flash'+'back'='FLASHBACK'
'of' acts as a link.
(Other definitions for flashback that I've seen before include "Film scene from an earlier time" , "Scene depicting previous events" , "Disturbing sudden vivid memory of a past event" , "(In film or novel) return to a previous event or period" , "Past scene re-enacted" .)