While human reaction time (and ability to actually see a bullet) is the most important factor, force and acceleration are also problematic.
Let’s assume a bullet is fired from 100 meters away at a person with perfect reaction time. Call the muzzle velocity 1000 meters per second. To move (say) 30 centimeters out of the way in 1/10th of second, a person would have to accelerate at 60 meters per second per second, assuming (unrealistically, but what the hey) instant acceleration.
Usain Bolt’s peak acceleration is around one G, and that is from starting blocks, not standing up straight. From a vertical posture, if you want to accelerate sideways at 6G, you have a big problem: when standing, your legs are optimized for keeping you vertical, not for sideways acceleration. If you don’t trust the coefficient of friction (or the structural integrity) of your sneakers, you’re better jumping over the bullet, not trying to move sideways. (Ducking, your maximum acceleration would be one G, unless you grabbed something on the ground and pulled.)
