That is a very good question. I've been there hundreds of time. The limiting factor is that you can't do any harm. I'm in health care (psychiatry) Are you in health care or law enforcement? Not being able to do any harm really makes this difficult. Here are some things I have tried from time to time. NOTHING I have tried works all the time or with any great consistancy in this circumstance. There is a lot of artistry. Do please post some of your ideas and maybe readers can add.

1) Attack a point on the opposite arm like the back of the elbow TW 11 and 12 and grab the hand you want to get when you get the cross extensor reflex.

2) Finger locks both the hyperextension type and the compression type. Be super careful about fracture.

3) TW 3 strike as supposed to be helpful but with this kind of resistance, and lack of desire to harm on our part, I find it overrated.

4) LI 5 or 6 rubbed with knuckles is truly annoying and might help.

6) Elbow rub front to back on Lv 13 or any other convenient torso point that will cause the opening up posture.

7) Lv 9 on the opposite quadrant leg. It takes the energy out of the hand you are manipulating. It will buy you a tempo to get the hand. Use it quickly.

I think the best ones are the ones where you don't go strength against strength with the hand. That is where his energy is and that is where he is braced for more pain than you are willing to inflict. I like the opposite quadrant ones best.
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The older I get, the better I was!