Artemis BJJ (MYGYM Bristol), Can Sönmez, Bristol, UK - 07/07/2017
You go for the sit-up as before, knocking into them with your hip. They manage to keep their balance and resist. Go with it, falling back. Previously, you were reaching over their shoulder to wrap up their triceps. With that arm, you're now going to lock their elbow tight to your chest. Grab their wrist with your other hand as you're falling back, grabbing your own wrist with your first arm.
Swivel perpendicular to their body, bringing your leg up their back to hold them in place. Push their wrist towards their head to finish the submission: you can twist your torso to do this, rather than relying on arm strength. Make sure you keep their upper arm clamped to your chest, to prevent them from using their hand to grab something. It's possible to break that grip and complete the kimura, but it's a complication best avoided.
You can also set this up by breaking their posture. If you are able to knock them sufficiently off balance, they may post out on their hands. That's the opening you're looking for: immediately sit up and latch onto their wrist, then complete the kimura as before.
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Teaching Notes: I showed this off the sit up sweep set up, briefly demonstrating the standard "if they're stupid and put their hand on the mat" entry too. I could have emphasised stopping their hand being able to grip the gi. The main way to do that is pin their elbow to your chest, a key point I highlighted, but it is easy to forget if you haven't done the kimura before. When there is space between your chest and their elbow, that tends to be where you lose it. Or alternatively, if you let them straighten out their arm. Naturally you can just switch to a pressing armbar or omoplata if that happens, but that's for a future lesson. ;)