MMA official (3)
I believe the answer is:
ref
'mma official' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ref that I've seen before include "Whistleblower (abbr)" , "One traditionally in black" , "'Game judge, in short (3)'" , "A diminutive umpire in soccer or boxing" , "In brief, a soccer controller" .)