Musician roasting nuts (8)
I believe the answer is:
organist
'musician' is the definition.
(I know that organist is a type of musician)
'roasting nuts' is the wordplay.
'nuts' indicates anagramming the letters (nuts can mean crazy).
'roasting' with letters rearranged gives 'ORGANIST'.
(Other definitions for organist that I've seen before include "Roasting (anag)" , "Church instr. player" , "Accompanist, keyboard player" , "It groans for church musician" , "One plays in church usually" .)