Accept post when head is sacked (4)
I believe the answer is:
take
'accept' is the definition.
(to accept is to take possession of)
'post when head is sacked' is the wordplay.
'post' becomes 'stake' (synonyms).
'when head is sacked' means to remove the first letter (the head of the word is removed or sacked).
'stake' with its first letter taken away is 'TAKE'.
(Other definitions for take that I've seen before include "Remove; capture" , "Subtract; assume" , "Accept, receive" , "Capture, secure" , "Procure" .)