One judge is up in arms (5)
I believe the answer is:
irate
'up in arms' is the definition.
(I've seen this in another clue)
'one judge' is the wordplay.
'one' becomes 'i' (Roman numeral).
'judge' becomes 'rate' (rating is a kind of judging).
'i'+'rate'='IRATE'
'is' is the link.
(Other definitions for irate that I've seen before include "having got in wax" , "Annoyed, nettled" , "Mad" , "Narked" , "raging" .)