Keep misdirecting the post (4)
I believe the answer is:
stop
'keep' is the definition.
(I know that stop is a kind of defend)
'misdirecting the post' is the wordplay.
'misdirecting' is an anagram indicator (I've seen 'misdirected' mean this (I've seen this in other clues)).
'post' with letters rearranged gives 'STOP'.
(Other definitions for stop that I've seen before include "Prevent - desist" , "End - period" , "Come to an end" , "Refrain from" , "oboe, perhaps" .)