Bill featuring in play, sycophant (5)
I believe the answer is:
toady
'sycophant' is the definition.
('toady' can be a synonym of 'sycophant')
'bill featuring in play' is the wordplay.
'bill' becomes 'ad' (advertisement stuck on wall).
'featuring in' is an insertion indicator.
'play' becomes 'toy' ('toy' can be a synonym of 'play').
'ad' going into 'toy' is 'TOADY'.
(Other definitions for toady that I've seen before include "Person who flatters and behaves obsequiously to another" , "Creep" , "Yes-man" , "Bootlicker" , "fawn" .)