Official character witness (7)
I believe the answer is:
referee
I believe this is a double definition.
'official' is the first definition.
(referee is a kind of official)
'character witness' is the second definition.
(someone providing a reference)
(Other definitions for referee that I've seen before include "Official to ensure fair play" , "Judge" , "Sports official" , "Game official" , "Match official" .)