Artemis BJJ (MYGYM Bristol), Can Sönmez, Bristol, UK - 15/04/2016
The triangle is a versatile submission you can do from almost any position, even underneath side control. For the mounted version, you need to trap one of their arms while clearing the other, just like any triangle. To force that position, bring your knee up high on one side, then on the other, pin their arm to their chest. Grab their head, kicking your leg through on the arm-pin side, swinging it under their head.
You can then base out with the arm that was pinning, in order to lean heavily to that side. Switch the hand you had under their head to your shin, pulling that up. Try and lock your other leg around the shin, creating the triangle lock. You can then thrust your hips and pull up on their head to finish, or move into an armbar or potentially an americana against your leg.
If you don't have the leg length or flexibility to get your legs locked (a common problem), maintain your grip on your shin. Use that to keep control as you roll through, finishing the triangle from guard.
Teaching & Sparring Notes: It's really hard to lock up the legs, so most people went for the rolling option. You need to lean a lot to get the necessary space to lock your legs. The other issue with this class is if people don't know how to do a triangle. I did some drills to introduce it, but if you've never seen a triangle before, then this is going to be hard. So perhaps this is something I should save for an 'advanced' class (which for me will just mean "requires prior knowledge") in future?