Gridiron judge (3)
I believe the answer is:
ref
'gridiron judge' 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 "In brief, a soccer controller" , "Whistleblower (abbr)" , "Sports umpire" , "One traditionally in black" , "Sports official (abbrev.)" .)