Bar snack from floor being picked up (4)
I believe the answer is:
nuts
'bar snack' is the definition.
(I've seen this in another clue)
'floor being picked up' is the wordplay.
'floor' becomes 'stun' (both can mean to shock).
'being picked up' shows that the letters should be reversed in order.
'stun' written backwards gives 'NUTS'.
'from' acts as a link.
(Other definitions for nuts that I've seen before include "Mad; seeds" , "Crazy (from Brazil?)" , "out to lunch" , "Beans" , "Edible seeds with hard shells" .)