Briefly a judge (3)

I believe the answer is:

ref

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'a judge' is the definition.
(referee)

I don't understand how the rest of the clue works.

(Other definitions for ref that I've seen before include "Whistleblower (abbr)" , "In brief, a soccer controller" , "'Game judge, in short (3)'" , "Football official (colloq.)" , "One traditionally in black" .)

I've seen this clue in The Mirror.

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