Jeer Republican oaf (4)
I believe the answer is:
boor
'oaf' is the definition.
(thesaurus)
'jeer republican' is the wordplay.
'jeer' becomes 'boo' (I've seen this before).
'republican' becomes 'r' (abbreviation).
'boo'+'r'='BOOR'
(Other definitions for boor that I've seen before include "Barbarian" , "Lout" , "oik" , "Rough, bad-mannered person" , "Crude uncouth person" .)