The 21 Foot Rule (Not Really a Rule)
According to Massad Ayoob in his book Deadly Force – Understanding Your Right to Self Defense- Ability, Opportunity, and Jeopardy must exist for you to use Deadly Force. “The situation of immediate danger of death or crippling injury is normally determined by the simultaneous presence of three criteria. Different schools use different terminology, but the most widely used and court-proven standard has been in use for decades: Ability, Opportunity, and Jeopardy. Ability means that the assailant possesses the power to kill or cripple. Opportunity means he is capable of immediately employing that power. Jeopardy means that his actions and/ or words indicate to a reasonable, prudent person that he intends to do so and is about to do so.”
Everyone talks about the 21 foot rule this is part of Opportunity…..remember its a study, not a rule and you may only be able to introduce it in a legal situation or trial when you can prove that you had been trained about it and understood the drills prior to the incident. In Massad Ayoobs book “Deadly Force” he says “Be Trained! Training is discoverable, and therefore introducible to educate the jury”
Ayoob, Massad (2014-11-25) Deadly Force – Understanding Your Right to Self Defense
The Tueller Drill is a self-defense training exercise to prepare against a short-range knife or contact weapon attack when armed only with a holstered handgun. Sergeant Dennis Tueller, of the Salt Lake City, Utah Police Department wondered how quickly an attacker with a knife could cover 21 feet (6.4 m), so he timed volunteers as they raced to stab the target. He determined that it could be done in 1.5 seconds. These results were first published as an article in SWAT magazine in 1983 and in a police training video by the same title, “How Close is Too Close?”A defender with a gun has a dilemma. If he shoots too early, he risks being charged with murder. If he waits until the attacker is definitely within striking range so there is no question about motives, he risks injury and even death. The Tueller experiments quantified a “danger zone” where an attacker presented a clear threat. The Tueller Drill combines both parts of the original time trials by Tueller.
There are several ways it can be conducted:
The “attacker and shooter are positioned back-to-back. At the signal, the attacker sprints away from the shooter, and the shooter unholsters his gun and shoots at the target 21 feet (6.4 m) in front of him. The attacker stops as soon as the shot is fired. The shooter is successful only if his shot is good and if the runner did not cover 21 feet (6.4 m).
A more stressful arrangement is to have the attacker begin 21 feet (6.4 m) behind the shooter and run towards the shooter. The shooter is successful only if he was able take a good shot before he is tapped on the back by the attacker.
If the shooter is armed with only a training replica gun, a full-contact drill may be done with the attacker running towards the shooter. In this variation, the shooter should practice side-stepping the attacker while he is drawing the gun.
You can see the original article by Dennis Tueller at this link