Stalemate, perhaps, with game's castle defence (10)
I believe the answer is:
drawbridge
'castle defence' is the definition.
(I've seen this before)
'stalemate perhaps with game's' is the wordplay.
'stalemate perhaps' becomes 'draw' (stalemate is a kind of draw).
'with' is a charade indicator (letters next to each other).
'game' becomes 'bridge' (bridge is a kind of game).
'draw'+'bridge'='DRAWBRIDGE'
(Other definitions for drawbridge that I've seen before include "Castle's defence" , "Keep attachment" , "Defensive measure" , "Castle defence" , "Barbican may defend this" .)