You are ready to be thrown completely to the ground, and there is no defence or counter that you can do. And I make the dagger go far from your hand, because I know this art with every skill.
Your opponent is bearing down on you for this play to work best. Keeping your back straight, bend your knees, and drop your weight down very low to come right in underneath your opponent. They will be stabbing straight down on top of you.
Make a hooking block to jam the attack. Scoop your left hand underneath the attacking dagger, contacting your opponents wrist with the base of then thumb. As soon as you contact, roll your hand over, grabbing the wrist and absorbing the shock of the strike.
In dropping your weight, push your right hip forward. You cant really get too low for this, and you may even feel your right knee brushing the floor. Use this hip movement to assertively drive your right forearm behind your opponents knee. This will catch their thigh, lifting their foot slightly as shown in the picture. Pull your right arm back to your ribs. This will spin your opponent on the spot, causing them to fall on their back to your left side.
Turn to follow them as they fall. You still control their right hand. As they hit the ground, kneel on them with your right knee, pinning them down. Use your left thigh as a fulcrum for a lever made from their right arm. Push down with your left hand, breaking their elbow. With your right hand, strip their dagger, draw your own, or simply make a fist. Hammer away into their face until they stop moving.
Variations on this sweep can also be seen in the following plays.