This technique is being demonstrated by Oscar Daniotti, a BJJ black belt under Ricardo de la Riva in Brazil. He is the chief editor Faixa Preta Digital, an online BJJ magazine available in both English and Portuguese.
This is a technique that I can vouch for. It’s one of the techniques that I use all the time. I’ve even used it in competition when someone stood up in an attempt to pass my half guard. Passing the belt through his legs stopped the guard pass and gave me the sweep.
Study this sweep even if you train mostly without the gi. Transitioning to the single leg takedown is a fundamental Half Guard technique. You can initiate the attack yourself, or use it reactively when your opponent is trying to slide his knee out of your half guard. Turn in HARD, grab the leg, and stand up. Of course there’s a little bit more to it than that, but that’s the gist of it and it’s very similar to the movement shown below.
1: Oscar starts in half guard, underhooking with his right arm, and hooking his opponent’s left leg with his right leg
2: He reaches for his opponent’s belt and begins passing it down through the legs
Stephan’s note: you can also pass the hem or skirt of his gi through his legs if his belt isn’t available
3: From this angle you can see how the belt has been fed through the legs and into Oscar’s right hand.
4: Oscar posts on his left hand and starts withdrawing his left leg.
Stephan’s note: this movement is essentially identical to the basic technical standup movement of BJJ.
5:Oscar is now standing, still using the belt grip to maintain control of his opponent’s hips. He could finish the sweep here, but to be even more effective….
6: …he ducks his head under his opponent’s arm…
7: …until his head comes out the other side of the armpit. He controls the tricep/elbow area tightly.
8: At this point it’s easy to drive your opponent forward and stabilize the top position (in this case, the knee mount).