Translation
In this way, I want to throw you to the ground before the dagger reaches me. And if your dagger comes down the middle to strike me, I release my grip and your dagger will follow. So you cannot hurt me in this way because then, with plays of the remedy, I will make you suffer.
Explanation
Your opponent has foolishly grabbed you by the jacket before they are ready to strike. Take advantage of this lapse of judgement by pinning their hand to your chest with your left hand, as in the master play.
Step to the outside with your right foot. Drop your weight low, keep your back straight, and with a large sweeping motion, scoop your hand under their thigh and then straighten up as shown. There is no clear progression here, and one of three things could reasonably be expected to happen, depending on the details of both combatants balance points in the moment.
If your opponent starts to fall forward, lift up your right hand, twist down with your left and volta stabile. Your opponent will fall on their face at your feet.
If they start to fall backwards, turn to the right and step through with your left leg, causing your opponent to fall on their back.
There is also the possibility that they will be be left balancing on one leg, and using their left hand to support themslves against you while still attempting a stab. In this scenario, throw their hand off to your left. This will turn their body away from you and jam the attack. Shuffle your left foot up to give you the appropriate distance, and with your right foot, make a round kick into the back of the knee on their supporting leg. Your opponent will drop straight down onto their tail bone.