I was rolling with this dude and got full mount. He didn't have much experience, but he was a little squirmy. So I grapevined his legs, pressed down with my hips, and arched my back. The intent was simply to stablize my position for a second while stretching my partner out and making it a little uncomfortable for him. However, he tapped from the grapevine. :redface: My instructor said that was a dangerous submission on the knees - one of those you don't do in practice but are good in competition (like heal hooks and some neck cranks, I guess). However, I never heard of this submission before, and I was simply trying to stablise my position. What kind of sub is this, what's its name, and how do you properly peform the technique (I don't count accidents as knowing how to do it)?