Repartee, as such, involving one with banner (10)
I believe the answer is:
persiflage
'repartee' is the definition.
(persiflage is a kind of repartee)
'as such involving one with banner' is the wordplay.
'as such' becomes 'perse' ('per se' can be a synonym of 'as such').
'involving' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'with' means one lot of letters go next to another.
'banner' becomes 'flag' (I've seen this before).
'i'+'flag'='iflag'
'perse' enclosing 'iflag' is 'PERSIFLAGE'.
(Other definitions for persiflage that I've seen before include "Light-hearted banter" , "Pale griefs (anag) - flippancy" , "Frivolous talk" , "Railing" , "Badinage, banter" .)