The guard player is playing guard with a shallow De La Riva hook, the guard passer is looking to pressure the guard position.
At 0.12 notice that the hand is cupping the calf and the guard player’s butt is inside the foot making it easy for the guard passer to point the toes outside which allows the knee to turn out, effectively killing the hook. The guard passer can then collapse the guard structure and step over to pass.
At 0.18 the guard player cups the heel keeping the elbow close to their body and low to the floor.
At 0.19 the guard player lifts their hips and sits on the foot. This action coupled with pulling the heel in a slight circular motion towards them makes it almost impossible to turn the toes outward therefore unable to turn the knee outwards so the guard structure remains strong.