Wrongdoers cease interrupting proposals (9)
I believe the answer is:
offenders
'wrongdoers' is the definition.
('offender' can be a synonym of 'wrongdoer')
'cease interrupting proposals' is the wordplay.
'cease' becomes 'end' ('end' can be a synonym of 'cease').
'interrupting' is an insertion indicator.
'proposals' becomes 'offers' (I can't explain this - if you can you should give a lot more credence to this answer).
'end' inserted inside 'offers' is 'OFFENDERS'.
Can you help me to learn more?
(Other definitions for offenders that I've seen before include "Wrongdoers" , "Lawbreakers" , "Miscreants" , "They break the law" , "Perhaps thieves" .)