Ah, I can tell you which one that was based on my arm position.
My "go to" lock is a "v-grip" lock and that's the one I did. It puts a tremendous amount of pressure on the tibia. Hyperextension of the ankle in this lock is bonus.
I can't tell you if it would actually break the tibia, but it sure feels like it. That's why it appears as if the fellow's ankle wasn't hyper'd out at all.
It's a bit hard to explain, but for my it works much better than the classic straight ankle lock. It took some time for me to perfect it, and involves quite a bit of "angle-ology" as Lloyd used to put it. Apparently, that's a Sambo term that doesn't translate well from Russian to English.
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