Has a choice sort of post (4)
I believe the answer is:
opts
'has a choice sort' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'of post' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'post' with letters rearranged gives 'OPTS'.
Can you help me to learn more?
(Other definitions for opts that I've seen before include "Elects" , "Picks needed" , "Settles" , "Selects as an alternative" , "Makes choice from post" .)