Surprise to see crazy coming back (4)
I believe the answer is:
stun
'surprise' is the definition.
(stunning is a kind of surprising)
'crazy coming back' is the wordplay.
'crazy' becomes 'nuts' (I've seen this before).
'coming back' is a reversal indicator.
'nuts' back-to-front is 'STUN'.
'to see' is the link.
(Other definitions for stun that I've seen before include "Shock, flabbergast" , "Knock unconscious" , "Daze or bewilder" , "Stagger, amaze" , "Knock into a semi-conscious state" .)