Disorderly Irish customer frequently in pub (9)
I believe the answer is:
irregular
'disorderly' is the definition.
(thesaurus)
'irish customer frequently in pub' is the wordplay.
'irish' becomes 'IR' (abbreviation for Irish).
'customer frequently in pub' becomes 'regular' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ir'+'regular'='IRREGULAR'
Can you help me to learn more?
(Other definitions for irregular that I've seen before include "Lacking continuity or contrary to the rule" , "Uneven - inappropriate" , "volunteer" , "member of the Baker Street contingent" , "Unconventional" .)