Publican popular with new guard (9)
I believe the answer is:
innkeeper
'publican' is the definition.
(a publican runs a pub)
'popular with new guard' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'with' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'guard' becomes 'keeper' (someone keeping or guarding something).
'in'+'n'+'keeper'='INNKEEPER'
(Other definitions for innkeeper that I've seen before include "Job" , "Pub licensee" , "Tavern owner" , "local manager" , "Manager who made extra provision for visitors" .)