One persevering as a judge? (5)
I believe the answer is:
trier
I believe this clue is a double definition.
'one persevering' is the first definition.
(I've seen this before)
'a judge?' is the second definition.
(trier is a kind of judge)
'as' is the link.
(Other definitions for trier that I've seen before include "Persevering type" , "German town, the capital of the northern empire in Roman times" , "Determined person" , "home for some Germans" , "Person attempting" .)