Disorderly Irish sort often in pub (9)
I believe the answer is:
irregular
'disorderly' is the definition.
(thesaurus)
'irish sort often in pub' is the wordplay.
'irish' becomes 'IR' (abbreviation).
'sort often in pub' becomes 'regular' (regular visitor to a pub).
'ir'+'regular'='IRREGULAR'
(Other definitions for irregular that I've seen before include "Against the rules" , "unprincipled" , "Not even or balanced" , "one of Holmes's Baker Street urchins" , "unlike full-time soldiers" .)