A bad American playwright (6)
I believe the answer is:
oneill
'american playwright' is the definition.
'O'Neill' can be an answer for 'playwright' (Eugene O'Neill, American playwright 1888-1953). I'm not sure about the 'american' bit.
'a bad' is the wordplay.
'a' becomes 'one'.
'bad' becomes 'ill' (similar in meaning).
'one'+'ill'='ONEILL'
Can you help me to learn more?
(Other definitions for oneill that I've seen before include "American dramatist" , "Eugene ..., Tip..., Ryan ... (1'5)" , "Eugene --, US dramatist" , "Eugene -, US playwright (The Iceman Cometh)" .)