Unionist politician's anger with southern judges (7)
I believe the answer is:
umpires
'judges' is the definition.
(umpiring is a kind of judging)
'unionist politician's anger with southern' is the wordplay.
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'politician' becomes 'mp' (Member of Parliament).
'anger' becomes 'ire' (synonyms).
'with' says to put letters next to each other.
'southern' becomes 'S' (abbreviation).
'u'+'mp'+'ire'+'s'='UMPIRES'
(Other definitions for umpires that I've seen before include "Sports adjudicators" , "they want fair play" , "Officials at cricket match" , "Referees for cricket marches" , "Officials at cricket matches" .)