Ban a professional writer (9)
I believe the answer is:
proscribe
'ban' is the definition.
(I know that ban is a more specific form of proscribe)
'a professional writer' is the wordplay.
'a professional' becomes 'pro' (abbreviation).
'writer' becomes 'scribe' (scribe is a kind of writer).
'pro'+'scribe'='PROSCRIBE'
(Other definitions for proscribe that I've seen before include "Exile" , "Denounce" , "Prohibit" , "Forbid; condemn" , "Ban" .)