]Jat Sau is a fundamental movement. It's found in its Siu Nim Tau form and it's also repeated in the Chum Kiu and in the wooden dummy form. Jat Sau means basically like a shock, or a small shock. The idea is that when you run into somebody's arm, for example if they're very big, if they're very strong, and you're not able to go through, you can actually use a Jat Sau to help disturb their position, or screw up their structure, so that you can continue punching.
So, Jat Sau actually works really good against people who are very tense, or very stiff. A real simple example is if you're in a fight, you encounter somebody's arms like this, and he's firing his biceps. He's using a lot of muscle force like this, or contractile force. All I need to do, is just do a very simple Jat action like this, and I can bring him forward like that.
Now, that opens a line for other punches and for follow-ups, but it basically works when I'm unable to go forward; his biceps are too tense, and I can use that against him, and it will open the line for a counter attack.
Now, when you practice the Jat Sau in the Siu Nim Tau form, it's very important that your Jat Sau goes straight down like this, and the force comes from the elbow, not from the wrist. Now Jat Sau should be done like an elevator, not like an escalator, all right? You see some people when they practice Wing Chun, they actually do the Jat Sau like this. The problem is, if I do a Jat Sau in this direction here, I'm actually drawing in to come and punch me, all right? And we don't want to draw our opponent into ourselves. We want to keep them away. So, Jat Sau should actually go straight down like this.
Another example for Jat Sau is for example, is in Chi Sau sparring, or when you're practicing Chi Sau sparring, or when you're practicing Chi Sau, you might run into somebody's arm, and they're very tense, which is very common. People get nervous, or they tense up in Chi Sau, and that's the Jat Sau right there. You can use this to move him out of the way.
Now, I can use the Jat Sau with a grab. I can use it without a grab. There are many different forms. Jat Sau actually doesn't imply that it has to be done this way, or this way, or thumbless or whatever. Jat Sau is actually the action, the jerk action of the hand is what we call Jat Sau. So it can come in different forms in fighting, and in Chi Sau.