When special forces do wrong with a hitman (8)
I believe the answer is:
assassin
'hitman' is the definition.
(I've seen this before)
'when special forces do wrong' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'special forces' becomes 'sas' (I've seen this in other clues).
'do wrong' becomes 'sin' (to sin is to do wrong or act badly).
'as'+'sas'+'sin'='ASSASSIN'
'with a' acts as a link.
(Other definitions for assassin that I've seen before include "One making hits" , "Booth, for example" , "A killer of political or religious leader" , "Murderer (of prominent figure)" , "hit man" .)