Traitor; defector (8)
I believe the answer is:
renegade
This clue is a double definition.
'traitor' is the first definition.
(I've seen this before)
'defector' is the second definition.
(I know that renegade is a type of defector)
(Other definitions for renegade that I've seen before include "Apostate" , "A deserter from a cause or faith" , "Treacherous person" , "Treacherous deserter" , "not someone true to the cause" .)