Prize fighting restricted by bill (5)
I believe the answer is:
award
'prize' is the definition.
('award' can be a synonym of 'prize')
'fighting restricted by bill' is the wordplay.
'fighting' becomes 'war'.
'restricted by' means one lot of letters goes inside another (I've seen this in other clues).
'bill' becomes 'ad' (advertisement stuck on wall).
'war' inserted inside 'ad' is 'AWARD'.
(Other definitions for award that I've seen before include "Judicial decision" , "Allotment" , "Honour, accolade." , "Give officially as prize or payment" , "Official prize in a draw" .)