Defending the Double Leg
>>>What is a good WC technique for stopping a takedown like a double-leg?<<<
The first thing to understand is that a good takedown artist isn’t going to try and double leg you rushing from across the room - he’s going to set up the shoot with strikes or from the clinch. Once he feels like he’s got a direct path to your lower body he’ll quickly change levels and take the shot.
There is one of the first keys - taking control of the fight enough that he can’t change levels, or if he does he’s too far away for the shot to have much power and opening a gap you can fill with your hands.
Let’s say he’s done a good job of leading your hands forward, changed levels, and is in full shoot – what you don’t want to do is try and stop him with strikes. Why? Because landing a power hit (something hard enough to end the shot) on someone coming fast at your legs underneath your arms is an extremely high-percentage move (meaning it’s unlikely, but not impossible).
The reason I say this is because of the mechanics involved in the whole operation. You know that kinetic power is derived from the momentum created by accelerating an object of mass. Because a good shot comes from a complete full-body commitment, you’ll understand that your punch is trying to stop the shooter’s entire body mass. That’s why, when they find the path, most grapplers can cut right through counter-punching attempts when shooting.
That’s why I don’t wager on that one “perfect” punch that will drop someone coming in like that.
Here’s another thing – from my own personal observations I think that a lot of the power and effectiveness in a move like the double leg comes from a good portion of the victim’s own involuntary reactions to it. When someone shoots in on you like that there is often an involuntary reaction to stand up and move away from the attack. Because you are “flinching up and away” you are actually doing a great deal of the work on getting your back slammed onto the ground.
[One a side note: the reverse side of this, in a stand up “striking” environment, is seen when you are throwing blows at someone who hasn’t undergone serious conditioning training. A poorly conditioned fighter will involuntarily pull his head back and his shoulders up in response to a committed, powerful punch. This reaction aids the Wing Chun fighter who knows how to pressure forward with solid footwork and follow up his strikes (chain punching).]
This is where a wrestler’s sprawl comes in. They use that natural reaction to throw their hips backward, but instead of “lifting” they sink their weight into the shooter – using their commited body mass in a superior (“top”) position to smother the power of the shot, which of course works great.
The thing is, there is no “wrestler’s sprawl” in Wing Chun. So, what do you do? One answer is to go “sprawl shopping” at your local wrestling club to pick up the defense, or maybe look deeper into your Wing Chun for something that may work just as well…
OK, from a Wing Chun standpoint, you most definitely can’t move back and, for argument’s sake, you don’t have the option of sprawling.
Now, here’s the interactive portion of my post: stand in your neutral stance (Ding Ma) – pretending someone was standing at your bridge, changed levels, and is now in full shoot – then quickly and ballistically shift your hips and center of gravity to one leg (it doesn’t matter which leg if he’s coming in straight for a double leg, but it’s more effective if you’re good enough with your footwork to follow his body movement and shift so you’re facing whichever side he has decided to place his head).
Note: the shooter WILL grab your legs - there just ain’t no gettin’ around that - BUT, the hip shift will redirect the force of the shot and spin him a little bit (just like how a bullfighter twists out of the way of a charging bull).
Now of course, just shifting your hips over to one leg will nullify - to a certain degree - the immediate danger of the double leg, if he’s worth his salt in takedowns he’ll just change up to a single leg and dump you anyway.
Therefore, once you shift your hips, you immediately drop your weighted knee (almost like a rapid squatting motion) while simultaneously using a Pak Sau (also called Gum Sau in this instance, which means “Pinning Hand”) motion with your arm to push the shooter’s body weight toward the ground.
What you have just done is called Cho Jum Ma, or “Shifted Sinking Stance”.
BUT DON’T STOP THERE!
Once you’ve shifted, sunk, and propelled the shooter’s body to the ground you have to pressure forward with the weighted knee into the shooter’s body to keep him from dropping his hands to your ankles, sucking his knees up, and single-legging you down.
When you pressure your weighted knee forward into his body you will find yourself pinning the shooter to the ground with your knee. That’s the magic of them there 100/0 “one-legged” stances.
From there it’s time to administer a grevious and severe @ss whoopin’ on the offending shooter.
BTW, all the body mechanics for this move are found in Chum Kiu.

One is weak because he makes preparation against others;
he has strength because he makes others prepare against him.
– Sun-Tzu