If he is able to turn around, spot the weapon, lift his arm, grasp the weapon, and lower his arm before Xavier can pull a trigger, he is superman and you shouldnt haver ****** him off in the first place.
No, not Superman, just practiced.
Many, many, many, MANY moons ago, my old sensei and I had a rather long chat about the virtues of 'Glock-Fu'. That is, the use of 9mm semi-automatic weapons platforms in close combat. My opinion, at the time, was that someone with a pistol would always win out on unarmed opponent. So he decided to show me differently.
We spent about two hours going through different scenarios. I was using a small cap pistol, a revolver, to simulate a .38. Face to face, he was able to relieve me of my 'weapon' about 8 out of 10 times, and this was while I was -expecting- him to take it. Then I decided to be cute.
As he turned away, I put the cap pistol to the back of his head. I intended to pull the trigger the moment that it contacted. I didn't have the opportunity.
The second the cap pistol touched his head he dropped low, breaking the line of fire to his head. He spun to his right, moving about 1-1/2 feet to my right, leading with his right hand, which closed on the 'weapon'. His left came up for a heel shot to my kidneys.
The next thing I knew I was on the ground, hurting, and my sensei has the cap pistol in his hands, and the biggest sh*t eating grin I've seen in a long time.
Now, the fact is that 96% of the population is not going to have that degree of training. And those that do are highly unlikely to be found committing an armed robbery. But the possibility does exist. Why risk it?