Amaze fans, making a comeback (4)
I believe the answer is:
stun
'amaze' is the definition.
(to stun is to amaze or shock)
'fans making a comeback' is the wordplay.
'fans' becomes 'nuts' (both can mean enthusiasts).
'making a comeback' says the letters should be written backwards.
'nuts' written backwards gives 'STUN'.
(Other definitions for stun that I've seen before include "Concuss; amaze" , "Render semi-conscious with blow" , "Dumbfound" , "Knock into a semi-conscious state" , "Daze, knock senseless" .)