Some madman, utter fanatic (3)
I believe the answer is:
nut
'fanatic' is the definition.
(I've seen this before)
'some madman utter' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'NUT' is hidden within 'madman utter'.
(Other definitions for nut that I've seen before include "Crank" , "Bolt securer" , "Fan" , "Combines with bolt to secure" , "Hard kernel of minutiae" .)