Marcelo answers Jon about the core's role in stabilizing posture when under attack: When playing from a Seated/Open Butterfly-Guard Position, keeping yourself upright is a vital part of maintaining both offense and defense; many of your countermeasures will involve keeping your posture vertical and employing Sit-Up style escapes, while staying close to your opponent rather than lying back on the mat will afford yourself many opportunities to attack in response to their pressure. If you feel your opponent try to shove and push you backwards, automatically project your feet outward and attempt to make contact with your soles onto their hips. If you can stick your opponent in front of you while still keeping upright, you will oftentimes find yourself in prime position for an upper body submission, e.g. a Guillotine Choke.