Cut down staff, getting sack (7)
I believe the answer is:
poleaxe
'cut down' is the definition.
(poleaxing is a kind of cutting down)
'staff getting sack' is the wordplay.
'staff' becomes 'pole' (I've seen this before).
'getting' says to put letters next to each other.
'sack' becomes 'axe' (both can mean to dismiss or cancel employment).
'pole'+'axe'='POLEAXE'
(Other definitions for poleaxe that I've seen before include "Shock greatly; weapon" , "Shock greatly; fell" , "Sharp old weapon" , "Knock down; shock" , "Halberd" .)