Some insane Roman fiddler? (4)
I believe the answer is:
nero
'fiddler?' is the definition.
(I've seen this before)
'some insane roman' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'NERO' is hidden within 'insane roman'.
(Other definitions for nero that I've seen before include "Roman emperor who fiddled while Rome burned" , "Wicked fiddler" , "Matricidal emperor" , "Famous fiddler" , "Ancient Roman emperor" .)