Making the first stopping shot with a speed of a “knock-out” punch is the highest level of any gun mastery and, in the same time, the highest necessity in an ambush - the worst case CQB scenario for a Close Protection Operative. As the late Col. Jeff Cooper put it: "you may need it once in a lifetime, but you will need it badly".
Technically, we are speaking of a shot delivered in the time frame of 1 second or less depending on the distance.