The arm drag from the overhook-underhook position is basically a clinch dump that capitalizes on the exact moment your opponent commits to a strike. When they throw that knee, they're standing on one leg. That's your window.
Here's the setup. You're in the inside-inside clinch -- both arms controlling biceps. You've been working the plum, fighting for position. Your opponent lifts a knee on the same side where you have bicep control.
The second that leg comes up, you underhook deep on that side and control the neck with your other hand. Then it's a steering wheel motion -- turn them downward. Done.
Why does this work so well? Because all their weight is on one base leg. They've voluntarily given up half their balance to throw that knee. A deep underhook plus a downward crank is more than enough to send them flying.
The key detail people miss: you need the neck control FIRST, before you go for the underhook. If you just underhook without controlling the head, they can posture up and fight out of it. Head control keeps them bent and off-balance while the underhook does the work.
Actually, the timing matters more than the technique itself. You can drill the underhook a thousand times, but if you can't read when that knee is coming, you'll never hit it live. Watch the hip. When it loads, that's your trigger.
For more clinch takedowns, dirty boxing entries, and the full overhook-underhook game, see our dirty boxing clinch techniques guide. Get the complete system in the Complete MMA Fighting System.