An interview with Tueller; well worth reading.
If you're not familiar, he's the man who got the question "How close does someone with a knife or club, something like that, have to be before he's a real threat?" and actually worked on it. Which produced what came to be called the '21-foot rule'(which he doesn't like; too hard & fast) and a lot more research into things like MOVING when someone is attacking. I'll steal one section:
Tueller: At the time, I was assigned to the Salt Lake City Police
Academy, conducting firearms and other use-of-force training. I was also
teaching part time at Gunsite. During an academy training session, we
had been doing draw-and-fire drills at the seven-yard line. During a
break, we were discussing use of force issues and one of the recruit
officers asked what to do if someone was attacking you with a knife, a
club, or some kind of a contact weapon. He wanted to know how close an
attacker should be allowed to encroach before the use of deadly force
was justified to stop him.
At first, I thought about saying three or four steps, but then I
realized that I didn’t have any idea how close was too close. I thought,
“We can do better that this!” Since we already knew the average time it
takes to draw, fire, and hit a target at seven yards – which was about 1
1/2 seconds from the holster – I decided to see just how long it would
take someone to cover that same distance.
So we had one recruit officer play the role of the “bad guy” and another
played the role of the “startled officer.” We put them 21 feet apart,
and when the bad guy role player decided to start his attack, we started
the stopwatch, and when the bad guy made contact with the good guy, we
stopped the watch. I was quite stunned to discover that the time was
roughly 1 1/2 seconds!
Then we tried the same exercise with everyone available in the class –
some younger, some older, big and small, male and female – and all of
them could run that seven yard distance in about 1 1/2 seconds. Of
course, this was before Simunitions® or Airsoft®, but later we did test
it with dart pistols. What we found was that if you’re ready and if
everything goes perfectly, you might get the gun out and get a shot off
before the bad guy role player makes contact. That is not good enough!
Shooting does not stop the action.
The bold is mine. Because this link was found in a thread on Facebook, wherein Larry Correia- who has a long record as a trainer for both LE and general citizens, wrote
the thing you are thinking of is the Tueller drill, based on the
research of Dennis Tueller from the SLCPD where he demonstrated that the
average person can cover 21 feet and inflict serious injuries with a
knife in the time the average officer could draw and fire. Keep in mind
that all handguns suck, and just because you put a round into somebody,
they don't always immediately stop doing whatever it is they are doing.