Outlaw supporting writer (9)
I believe the answer is:
proscribe
'outlaw' is the definition.
(thesaurus)
'supporting writer' is the wordplay.
'supporting' becomes 'pro' (I've seen this in other clues).
'writer' becomes 'scribe' (scribe is a kind of writer**).
'pro'+'scribe'='PROSCRIBE'
(Other definitions for proscribe that I've seen before include "Forbid; condemn" , "Ban" , "Prohibit" , "Denounce" , "Exile" .)