Scoundrel supporting blocking refund (9)
I believe the answer is:
reprobate
'scoundrel' is the definition.
(I've seen this before)
'supporting blocking refund' is the wordplay.
'supporting' becomes 'pro' (being pro something is supporting it).
'blocking' is an insertion indicator (block can mean to plug a gap in something).
'refund' becomes 'rebate' (rebate is a kind of refund).
'pro' inserted into 'rebate' is 'REPROBATE'.
(Other definitions for reprobate that I've seen before include "Berate pro, being an unprincipled person" , "baddie" , "Rogue" , "Sinner" , "rake" .)