Party by Roman upset bouncer (7)
I believe the answer is:
doorman
'bouncer' is the definition.
(guard stationed at a door)
'party by roman upset' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'by' means one lot of letters go next to another.
'upset' is an anagram indicator.
'roman' is an anagram of 'orman'.
'do'+'orman'='DOORMAN'
(Other definitions for doorman that I've seen before include "hotel employee?" , "Entry attendant" , "Commissionaire" , "One who may help guest" , "Entrance attendant" .)