Clerk in high spirits, entertaining new escort (9)
I believe the answer is:
penpusher
'clerk' is the definition.
(penpusher is a kind of clerk)
'high spirits entertaining new escort' is the wordplay.
'high spirits' becomes 'pep' (both can mean enthusiasm or energy).
'entertaining' is an insertion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'escort' becomes 'usher' (usher is a kind of escort).
'pep' placed around 'n' is 'penp'.
'penp'+'usher'='PENPUSHER'
'in' acts as a link.
(Other definitions for penpusher that I've seen before include "Hen supper for an old scribe or lowly clerk" , "Clerical worker with a boring job" , "Bored clerk" , "Clerical worker with a tedious job" .)