Crazy about shock (4)
I believe the answer is:
stun
'shock' is the definition.
(both can mean to surprise)
'crazy about' is the wordplay.
'crazy' becomes 'nuts' (nuts can informally mean crazy or mad).
'about' shows that the letters should be reversed in order.
'nuts' back-to-front is 'STUN'.
(Other definitions for stun that I've seen before include "Knock into a semi-conscious state" , "Concuss, stupefy" , "Daze, knock senseless" , "Astound; render senseless" , "Anaesthetise" .)