"Kickass Kungfu" or realtime optical motion capture
There's a lot of videos in their video section. A person stands in front of two screens and their shadow gets scanned in realtime and analyzed. Then it is projected into two-dimensional game screen.
The problem with this stuff is of course that it requires the large, sweeping movements and athleticism of something like choreographic kung fu or tae kwon do.
The thing that seems to matter the most is the vertical position of the body. Jumping helps avoid being hit, of course. Something that utilizes very refined and multi-dimensional body movement, such as aikido, would be a complete loss to this program as it does not handle any sort of contact except the hits and does not operate in 3D. You can't sidestep an attack, due to the obvious 2D limitation. You can't catch an enemy's foot with your hands, or redirect their punch. Yada yada.