A judge of rarebit, perhaps (7)
I believe the answer is:
arbiter
'a judge' is the definition.
(I know that arbiter is a type of judge)
'rarebit perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'rarebit' with letters rearranged gives 'ARBITER'.
'of' is the link.
(Other definitions for arbiter that I've seen before include "Judge, final authority" , "Mediator or referee" , "Rear bit (anag.)" , "Judge - mediator" , "Settler of dispute" .)