as soon as they dive under, dig for am underhook, lock your palms with the gable grip and press the elbow of the far side arm in front of their face. that makes it
very difficult for them to continue with the pass. for instance, he gets both of his arms under my legs, i shoot my left hand under his right armpit, reach over with my right hand and gable grip my left hand. i then use my right to pull my left as deep inside as i can and press my right elbow in front of their face.
once you have that, you can attack in a few different directions.
- the first thing i try is to kick the leg on the side that i'm underhooking them. so my left is underhooking and my right is pressing their face, i kick my left leg downwards as i use the underhook to pull his shoulder upwards. this motion jerks their arm back inside and you have a nice triangle.
- you can also attempt to simply switch the angle, feed your right shin to your right hand grip and lock up an armless triangle. it looks stupid, but it's effective as hell and will put people to sleep very quickly.
- i've also done a sort of armless omoplata where you just swing into the regular omoplata motion, but the pressure on their shoulder is done with your underhook rather than your thigh, but this is mostly to just off-balance them.
braulio explains an armbar from this position here and you can clearly see the triangle like right there for the taking as soon as he clears the arm:
and here's a pretty crappy video of a guy showing the armless triangle to someone. not exactly high quality stuff but enough to get the basic idea: