I'm shooting a video lesson this weekend for the online school -- a video that goes over the three main goals of internal self-defense, particularly Tai Chi and Baguazhang.
Hsing-I utilizes many of the principles of internal fighting, but the primary goal of Hsing-I is to take your opponent's ground and drive through him.
Tai Chi is more like a beach ball floating in water. If you jump on the ball, it gives a little, then it bounces back and spirals you into the water. There's really very little you can do about it once you jump on the ball.
Bagua is similar to a wire ball that's spinning. If you punch into the wire ball, you'll get caught up and flung out in any direction.
There are three goals of self-defense that are very similar in Tai Chi and Bagua:
1. Uproot -- your opponent is rooted but your goal is to uproot him. There are several ways of doing this, but two primary methods are pushing upward (starting under his center of gravity) or bumping with the shoulder, hip, and body.
2. Unbalance -- when your opponent goes off-balance, it opens a window of opportunity. We call it a "moment of vulnerability" when you have dissipated his force and can counter-attack. This can be done in a variety of ways. You can simply remove the target and not allow his force to find it's target. You can use closing techniques with your feet to break his root and unbalance him. Movements such as "walking obliquely" in taiji and "sweep the rider from his horse" in bagua unbalance the opponent and take them down.
3. Control the Center -- Where you opponent's center is going -- you want to keep it going that way. The old Taoist saying "do not contend" applies here. Go with the flow. Step into your opponent's center. Allow your center to become One with your opponent's center. Then control his center. Move with his center and when you take control, you take him down.
The photos show intercepting a punch and applying "supporting" or "upward" energy to uproot the opponent. There are several techniques that show this in a real way. These are all physical skills that require practice thousands of times.