Writer agitates mad artist (9)
I believe the answer is:
dramatist
'writer' is the definition.
(I know that dramatist is a type of writer)
'agitates mad artist' is the wordplay.
'agitates' indicates anagramming the letters (I've seen 'agitating' mean this).
'mad'+'artist'='madartist'
'madartist' with letters rearranged gives 'DRAMATIST'.
(Other definitions for dramatist that I've seen before include "Coward perhaps" , "man of theatre" , "Shakespeare, say" , "Coward, for example" , "Wordsmith" .)