http://www.youtube.com/watch#!v=2cFhnh9NK2E&feature=related
Very good.
At 45 seconds the guy does the exact rear punch/takedown combo I used in competition. The version I learned is from Xingyiquan's Chicken Form, "Golden Rooster Announces the Dawn."
Worked very well for me.
That takes some balldacity.
It's a good thing karate "isn't good for fighting" cause some of this stuff looks pretty scary.