The manual, which I read while I was downloading new sound and video drivers(If you have a Dell and Santa Cruz audio card, don't download a new driver from Dell...TRUST ME!!), states: "You can be knocked down during combat as the result of a powerful blow from an opponent. A knockdown is fairly short and can happen at any time,regardless of your Health or Fatigue levels. You cannot block or attack when you have been knocked down. Hitting someone who is knocked down does more damage and they are easier to hit. **High Agility keeps you from being knocked down**"
There you have it, Agility will set you free. I've also found that having 90 Speed and getting to hit first seems to keep me a tad safer as well...if they can't hit you, you can't be knocked down
