http://www.suarezinternational.com/evasionfootwork.html
Excerpt:
The concept of getting off the "x" allows the good guy to evade an onrushing contact weapon attacker for a moment in time. This allows the good guy to deploy the gun and get a couple of shots into the bad guy. This can happen at any distance. Predominantly, it is within 5 yards.
The issue quickly becomes "what if those shots didn't work immediately". The good guy has moved off the line of attack, but although he may have been shot already, the bad guy begins to adjust to track him. Given how quickly the attacker can cover ground (7 yards 1.5 seconds, 5 yards 1.0 seconds, 3 yards .75 seconds, 2 yards...well, you get the idea) even if you evade the initial attack, the distance is now so close that he can reach you as soon as he adjusts his line. No ammo fired from any weapon will drop a man in his tracks with any certainty. Certainly not enough to forget about back up plans. We want to answer the question - what if I've hit him and he's still coming?
You certainly don't want to stand there looking at your museum piece bar-b-que gun wondering why the guru was wrong!
...