One judge could be cross (5)
I believe the answer is:
irate
'be cross' is the definition.
(thesaurus)
'one judge' is the wordplay.
'one' becomes 'i' (Roman numeral).
'judge' becomes 'rate' (rating is a kind of judging).
'i'+'rate'='IRATE'
'could' is the link.
(Other definitions for irate that I've seen before include "Boiling" , "Magical rod" , "I tear away, being annoyed" , "having got in wax" , "Annoyed, irritated" .)