Unsheathe and turn to parry with (4)
I believe the answer is:
draw
'unsheathe' is the definition.
(as in drawing a sword)
'turn to parry with' is the wordplay.
'turn' shows that the letters should be reversed in order.
'to parry' becomes 'ard' (I can't justify this - if you can you should believe this answer much more).
'with' becomes 'w' (short for with).
'ard' reversed gives 'dra'.
'dra'+'w'='DRAW'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for draw that I've seen before include "Take in (a breath), attraction" , "Design" , "Snag" , "Tie - attract" , "Extract" .)