Stop pubs hosting 'unlimited hour' — it's vulgar (9)
I believe the answer is:
barbarous
'it's vulgar' is the definition.
(thesaurus)
'stop pubs hosting unlimited' is the wordplay.
'stop' becomes 'bar' (bar can mean to stop or prevent).
'pubs' becomes 'bars' (a bar is a pub).
'hosting' is an insertion indicator (inserted letters are welcomed in or hosted).
'unlimited' becomes 'ou' (I am not sure about this - if you are sure you should believe this answer much more).
'bars' going around 'ou' is 'barous'.
'bar'+'barous'='BARBAROUS'
'hour' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for barbarous that I've seen before include "Brutal; uncivilised" , "Savage" , "Exceedingly brutal" .)