Mad artist turns playwright (9)
I believe the answer is:
dramatist
'playwright' is the definition.
(I know that playwright can be written as dramatist)
'mad artist turns' is the wordplay.
'turns' indicates anagramming the letters.
'mad'+'artist'='madartist'
'madartist' anagrammed gives 'DRAMATIST'.
(Other definitions for dramatist that I've seen before include "Coward perhaps" , "Writer of plays" , "Wordsmith" , "Pinter, say" , "man of theatre" .)