Briefly judge (3)
I believe the answer is:
ref
'judge' is the definition.
(referee)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ref that I've seen before include "A diminutive umpire in soccer or boxing" , "Football's whistler" , "One traditionally in black" , "In brief, he controls a soccer match" , "Middleman needing cards" .)