This grip is so strong that I believe I can kill anyone with it, because I can break your arm and I can throw you to the ground, and I can take your dagger. I can also tie you in the high bind. And from these four things, you will not be free.
Although it sits within the dagger section, this is essentially a grappling technique. It works especially well against an overhead hammerfist style attack, such as is delivered with a mandritto or fendente dagger strike. The real key to making this work is to catch the attack after it has been chambered, but before it has been properly launched. As with all grappling techniques, timing and flow are critical.
With your left arm, make an upper block to jam your opponents dagger hand. You want their forearm to be no further forward than upright if possible. Make initial contact with the outside of your forearm and roll it roll it so your palm faces away from you.
Quickly step through with your right foot. You will need to get in close. Use the hip rotation to throw your right arm under your opponents right arm. Reach up with your right hand and grab on to your left hand.
You have now created a crank handle as pictured. Your opponents upper arm rests in the crook of your right elbow, creating a pivot point. Their forearm is a lever, which you about to push back and down.
Step through with the left foot, giving your body a slight clockwise twist. You want to lever the forearm past your opponents shoulder and behind them. If it goes too wide, and the angle of the arm exceeds 90 degrees, they have a chance to twist free. Keep it tight.
Lock your right elbow onto your hip and push your hand straight down. This will apply a great amount of torsional leverage to your opponents shoulder. If their knees dont give way first, it will tear the shoulder joint. Either way, your opponent will fall straight down in a crumpled heap at your feet.