They slap hands, then it’s all about grip fighting. Notice how Marcelo simply will not accept his opponent getting good grips. He keeps trying to break the collar grip until he succeeds by leaning his weight backwards as he pushes away with his foot on the mat. Rafael retreats and stands up, then re-engages, looking for his trademark knee slide pass.
The way Marcelo defends this is very interesting. It initially looks like Rafael has passed, but Marcelo posts on his right elbow, giving him the space to thread his left foot in over the top of Rafael’s lead leg, he then inserts it in further, under the opposite leg to prevent the guard pass from completing, and ends up back in a (slightly flattened) butterfly guard. That’s an impressive defence to a very difficult-to-defend pass. This elbow post is a key part of Marcelo’s Sit Up defence to regaining guard.