Musician to resign unexpectedly (6)
I believe the answer is:
singer
'musician' is the definition.
(I know that singer is a type of musician)
'resign unexpectedly' is the wordplay.
'unexpectedly' is an anagram indicator.
'resign' with letters rearranged gives 'SINGER'.
'to' acts as a link.
(Other definitions for singer that I've seen before include "Someone of note" , "Vocalist" , "Entertainer" , "Crooner" , "choirboy?" .)