Knight using advantage to snaffle unprotected pawn (6)
I believe the answer is:
gawain
'knight' is the definition.
(Sir Gawain is a knight in Arthurian legend)
'advantage to snaffle unprotected pawn' is the wordplay.
'advantage' becomes 'gain' (gain is a kind of advantage).
'to snaffle' indicates putting letters inside (snaffle can mean to take or steal).
'unprotected' means to look at the middle letters.
The centre of 'pawn' is 'aw'.
'gain' enclosing 'aw' is 'GAWAIN'.
'using' is the link.
(Other definitions for gawain that I've seen before include "round a table for him and his comrades?" , "One of King Arthur's knights" , "Man at round table" , "Arthurian knight of the Round Table" , "K" .)