Flipping stone cask for spice (6)
I believe the answer is:
nutmeg
'for spice' is the definition.
(nutmeg is a kind of spice)
'flipping stone cask' is the wordplay.
'flipping' shows that the letters should be reversed in order.
'stone' becomes 'gem' (a gemstone).
'cask' becomes 'tun' (tun is a kind of cask).
'gem'+'tun'='gemtun'
'gemtun' written backwards gives 'NUTMEG'.
(Other definitions for nutmeg that I've seen before include "Kick the football between an opponent's legs" , "(In soccer) kick the ball between an opponent's legs" , "it's used by bakers" , "Spice for grating" , "Hard aromatic seed" .)