Astound by throwing nuts (4)
I believe the answer is:
'astound' is the definition.
(I've seen this before)
'throwing nuts' is the wordplay.
'throwing' indicates anagramming the letters.
'nuts' anagrammed gives 'STUN'.
'by' acts as a link.
(Other definitions for stun that I've seen before include "Daze, overwhelm" , "deliver a knock-out blow" , "Surprise greatly or daze" , "Render semi-conscious with blow" , "Amaze; knock senseless" .)