American bill to stop college group campaigning (9)
I believe the answer is:
crusading
'campaigning' is the definition.
(crusading is a kind of campaigning)
'american bill to stop college group' is the wordplay.
'american' becomes 'US' (abbreviation for United States).
'bill' becomes 'ad' (advertisement stuck on wall).
'to stop' is an insertion indicator (stop can mean to plug a hole in something).
'college' becomes 'c'.
'group' becomes 'ring' (a ring is a criminal organisation).
'us'+'ad'='usad'
'c'+'ring'='cring'
'usad' put inside 'cring' is 'CRUSADING'.
(Another definition for crusading that I've seen is " campaigning".)