Cause amazement by juggling nuts (4)
I believe the answer is:
stun
'cause amazement' is the definition.
(I've seen this before)
'juggling nuts' is the wordplay.
'juggling' is an anagram indicator (I've seen this in other clues).
'nuts' is an anagram of 'STUN'.
'by' is the link.
(Other definitions for stun that I've seen before include "Nuts (anag)" , "Knock into a semi-conscious state" , "Daze, paralyse" , "'Shock, daze (4)'" , "Render temporarily senseless" .)