The Chair Sit is one of the most common techniques used to take someone's back in BJJ, and it can also be used to regain back control when you opponent escapes from it.
Escaping the Back is one thing, defending and preventing the hooks from being inserted in the first place is another.
This is one of the most common mistakes when trying to escape the Back Control, even high level BJJ black belts struggle with it.
It’s always safer to escape from the Back if you go to the UNDERHOOK side of the Seatbelt Grip, provided you have good head positioning. But sometimes, you won’t be able