This is the sixth, who wants to take the sword of the companion. When taking the sword, keep lifting straight up, and his sword will certainly fall from his hand.
This play takes place after the initial contact. Your swords will be crossed in the middle. From there, drop your right hand down, reaching across your opponent and rolling your blade to the opposite side of your opponents horse. Twist your body to do this rather than reaching across with your shoulders. If you lean too far, you are in danger of being tangled in your opponent and stripped from the saddle. You should find yourself in the position shown.
Having wedged your hand behind the pommel of your opponents sword, drop your weight into the saddle and pull your right elbow back across your body, raising your right hand as you do so. Although pulling your elbow back makes you more stable, it is the lift which actually strips the weapon.
The angle of your hand and pommel severely restricts the movement of your opponents sword hand. The higher you lift, the safer you are and the more your opponents fingers are pried open. The sword should fall behind your left shoulder, leaving you safe to turn and pursue your now cursing opponent.