I'm calling this the buddy choke because you execute it while side by side after defending a top half guard position from an underhook from the bottom.
Rodrigo has shown us a couple of similar moves from the top in half guard that involve this backstep. I remember a guard pass that had you backstep over the guy, walk yourself backward to clear space, then step back over to the other side and tuck your leg in, wedging your knee between your hips and his hips. From there, it is a lot like my current main half guard pass. Or a combination of that one and the version with the knee wedge that Saulo shows in his first DVD series.
So here, the guy on the bottom get the underhook. You hook the head with your forearm tight around his neck like you were going to do an Ezekiel.
Grab low on your lapel and feed it to your headhook hand. Then reach over and behind his head and grab your wrist with your far arm hand.
The choke comes from the lapel on one side and the forearm of your far arm on your other.
To get leverage, it is a good idea to walk your hips backward, towards his head, as if you were moving to north-south. That also makes it easy to throw your leg over and really add some torque to the choke.
There are two leg throw-overs that Rodrigo showed. The first is just over his far shoulder, sort of like you might do for a kimura finish. The second is all the way over his head, so that your leg is on "your" side of his head.
Both options create tremendous pressure on the neck. So it is a good idea to be careful when attacking with them.
