Regularly chop cold venison source, having withdrawn seafood (6)
I believe the answer is:
cockle
'seafood' is the definition.
(cockle is a kind of seafood)
'regularly chop cold venison source having withdrawn' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'cold' becomes 'c' (eg on taps).
'venison source' becomes 'elk' (venison is deer or elk meat).
'having withdrawn' shows that the letters should be reversed in order (letters draw back).
The alternating letters of 'chop' are 'co'.
'elk' written backwards gives 'kle'.
'co'+'c'+'kle'='COCKLE'
(Other definitions for cockle that I've seen before include "Common edible bivalve" , "Edible bivalve mollusc" , "Burrowing mollusc" , "occupant of shell" , "Seafood item" .)