The 21 Foot Rule: Forensic Fact or Police Myth?

Officers throughout the United States have heard use of force instructors discuss the “21 Foot Rule” during their officer safety, firearms and deadly force training. As a use of force instructor and a forensic police practices expert, I have trained and testified to this concept myself.

In 1983, the concept’s founder, Salt Lake City PD police firearms instructor Lt. John Tueller (Ret.) set up a drill where he placed a “suspect” armed with an edged weapon 20 or so feet away from an officer with a holstered sidearm. He then directed the armed suspect to run toward the officer in attack mode. The training objective was to determine whether the officer could draw and accurately fire upon the assailant before the suspect stabbed them. After repeating the drill numerous times, Tueller wrote an article wherein he opined that it was entirely possible for a suspect armed with an edged weapon to successfully and fatally engage an officer armed with a handgun within a distance of 21 feet. The “21 Foot Rule” concept was born and soon spread throughout the law enforcement community almost like a virus. It is interesting to note that even Tueller does not know where the term “21 Foot Rule” came from.

Tueller never imagined when he designed his simple firearms training drill that, 30 years later, the 21 Foot Rule would eventually become a police doctrine that is taught and testified to hundreds of times a year. So, is the 21 Foot Rule a forensic fact or a police myth?

If we are dealing with critical issues of officer safety and deadly force, it is important that we seek to arrive at the factual basis of any tactic which some consider to be steadfast dogma to see if it can be forensically defended during training and in court.

It is important to keep in mind that Tueller designed his firearms action-reaction experiment as a training device to assist his officer students in better understanding the concept of the reactionary gap. The reactionary gap is a human factors formula that compares action vs. reaction. In humans, sudden action is usually faster than a defensive response or reaction. In training and in actual high-risk encounters with armed and unarmed subjects, the closer an assailant is to an officer, the less time the officer has to defensively react to any aggressive action the assailant makes.

Information I have researched including actual video interviews with Lt. Tueller indicate that he never designed nor presented his firearms training drill as an organized, outlined and implemented research project involving the applied sciences of psychophysiology, physics and related human factors. No forensic testing, examination, reconciliation of data or scientific oversight of a research model was ever conducted.

During the past 30 years since the 21 Foot Rule has become an informal doctrine within the law enforcement community, I have heard it misstated, misrepresented and bastardized by use of force, firearms and police practices experts from all sides. I actually reviewed the fact pattern of an officer-involved shooting (OIS) case where an officer with a carbine fatally shot/killed a suspect armed with a knife from a distance of more than 150 feet, who attempted to use the “Tueller Drill” as his defense.

Instructors and experts also seem to have forgotten that the original premise of Lt. Tueller’s drill was that his designed circumstance involved an officer with a holstered sidearm drawing and accurately firing his weapon. In the vast majority of officer-involved shootings I have investigated or reviewed, the officer already had his gun not only out of its holster, but either at the “low ready” position or directly aimed at the suspect who was either armed with a knife or was furtively reaching into their waistband.

So what are the real forensic facts that might assist officers with their officer safety and deadly force determinations? Actually, there are no forensically proven facts that I am aware of that specifically verify or conclusively establish that a suspect armed with an edged weapon will, more likely than not, be able to seriously injure or kill an officer armed with a sidearm on all occasions and circumstances. The truth is that the 21 Foot Rule should not be considered to be an absolute rule at all because there are too many variables involved at this point to call it a “rule.” Let’s discuss them.

This is the study of how the brain influences and effects physiological function. Science tells us that humans possess both a forebrain and a midbrain. The forebrain is where cognitive processing and decision making takes place. The midbrain plays a role in situational awareness, sleep, arousal, alertness and trained and subconscious memories.

When a human (officer) experiences a threat, it takes, on average, 0.58 second to experience the threat and determine if it is real. It then takes, on average, 0.56–1.0 seconds to make a response decision. In animals, the responses are: fight, flight or freeze. However, humans have five responses: defend (fight), disengage (retreat), posture (yell, point a finger, act aggressive), become hypervigilant (panic, confusion, freezing, using force excessively) and submit (surrender).

When a human is threatened, the brain automatically infuses the body with adrenalin (stimulant), endorphins (pain blockers) and dopamine (euphoric pain blocker).

The body designed these chemicals to help us survive an encounter by making us faster, stronger and more pain tolerant. However, these same chemicals can also significantly diminish our human performance under intense stress by causing such problems as perceptional narrowing (tunnel vision), loss of near vision and auditory occlusion (reduced hearing) or exclusion (loss of hearing), among others. This ultimately negatively affects our chances of surviving a violent encounter.

Under the intense stress normally associated with deadly force threat scenarios and while under the influence of survival chemicals, the body’s basal metabolic rate, measured by heart rate, blood pressure and respiration, climbs significantly in milliseconds. This dynamic can cause further psychophysiological impairments such as vasoconstriction which can impair weapon manipulation, cognitive processing and stress memory recall following an encounter.

Equipment and competency as reaction factors
Several factors effect an officer’s survival against an attacker. For instance, an officer or detective whose sidearm is secured in a Threat Level III holster will certainly have a slower draw to target acquisition time than an officer drawing from a Threat Level I holster. An officer’s experience and competency with their holster system and combat shooting style are also critical human factors in an officer’s ability to draw, move off the line of attack and direct accurate fire upon an armed assailant.

Accuracy of fire at close distances
The average officer in static firearms qualifications (non-timed standing and shooting without moving) can hit the 9–10 rings far more often than not from the five yard line. However, research of actual OIS incidents has shown that officers can only accurately hit their moving assailants 14% of the time in life or death situations from distances of only two to 10 feet. On the other hand, assailants were able to successfully engage and hit officers 68% of the time within those same distances.  So the psychophysiological components of actual gun fighting play a critical role in an officer’s survivability within relatively close distances.

Start shooting to stop shooting: “Perception lag time”
Once the average officer gets on target, it takes them 0.56 seconds to make a decision to commence shooting. However, it then takes that same officer 0.25–0.31/100ths of a second per trigger pull to fire. As the deadly force scenario rapidly evolves, it takes that same officer on average 0.5–0.6 seconds to realize that the threat has passed and to stop shooting.  This is because of a psychophysiological dynamic referred to as “perception action—reaction lag time.” Another question we might ask (and would never know) is whether the officer’s brain processed the threat information serially, or if it was parallely distributed.

The subject of why suspects are found to have entry wounds in their sides and backs when an officer has asserted that the suspect was facing them when they fired is a bi-product of perception action-reaction lag time and the manner in which information was processed by the officer’s brain. This is pretty sophisticated information for a criminal or civil jury to understand and consider.

Adding it all up: Fantasy or forensic fact
The fields of contemporary police practices and applied sciences are rapidly changing methods. Applied science by its nature, supports or rejects hypothesis and theories based upon the reconciliation of scientific statements, facts and evidence. However, law enforcement is more inclined to be archaic and married to non-forensic, speculative dogma that often goes unchallenged, but becomes widely accepted as fact.

It is my opinion that Lt. John Tueller did us all a tremendous service in at least starting a discussion and educating us about action vs. reaction and perception–reaction lag. This has certainly saved many lives within our ranks. However, it is certainly time to move forward with a far more scientific analysis that actually seeks to support or reject this hypothesis.

The question as to whether or not the 21 Foot Rule is an applicable defense in an officer-involved shooting actually depends upon the facts and evidence of every unique and rapidly evolving deadly force encounter. In some circumstances, shooting at similar distances with far more experienced, competent and better equipped officers, within an environment with physical obstructions such as a police vehicle, might be inappropriate. Whereas, with inexperienced officers, wearing a difficult holster system and no obstructions within distances greater than 21 feet might be justified.

As the 1989 precedent use of force/deadly force U.S. Supreme Court ruling in Graham v. Connor (490 U.S. 386, 109 S.Ct) has eloquently stated, each high-risk encounter during a rapidly evolving situation is unique. My sense is that future research may underscore that legal principle with respect to The Tueller Drill.

Be safe out there!

Note: Special thanks to forensic expert team members Homicide Lt. Bob Prevot (Ret.), M.A., ballistic scientist/firearms expert Lance Martini, M.S., firearms expert Larr


Ron Martinelli, Ph.D., is a nationally renowned forensic criminologist specializing in police death cases, use of force, human factors and psychophysiology. Dr. Martinelli is a retired law enforcement officer who directs the nation’s only multidisciplinary civilian Forensic Death Investigation Team at Martinelli & Associates, Inc. He can be reached at 951-719-1450 and His firm is presently engaged in a major forensic scientific project reanalyzing the “21 Foot Rule.” If you are interested in volunteering for this important project, please contact his office.


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  1. TeeJaw

    The Tueller drills supplements one of the criteria in the 3-part analysis for deciding whether an attacker presents a threat of death or serious bodily injury. A knife in one’s hand gives him the ability. His demeanor determines the question of jeopardy and I’d day that a person holding a knife who will not respond to an officer’s command to drop the knife has established that he is a credible threat to the officer. The only question remaining is whether he has sufficent opportunity to carry out his threat. The Tueller drill shows that a person in good physical condition can present a deadly threat from a greater distance that commony believed. Maybe that is 21 feet, more or less, depending upon his or her physical condition and ability.

    So, a 78-year old woman holding up a butcher knife from 10 feet away against a 21-year track athlete does not likely present a deadly threat. A 21-year old who looks to be in top condition facing a 49-year old pot-bellied cop from 30 feet could very well constitute a deadly threat to the cop. Before Deniis Tueller’s research this was not so obvious.

  2. albundy57

    In the lawnesness with which we find the 2010’s, I would allow every officer to shoot to kill in any situation in which they are in fear with their life. No longer is presumption of innocence in the best interest of society since terroristd, criminal gangs, and corrupt legal system & judicial units is so widespread. And these officers should be given awards for killing violent drug dealers not punishment or incarceration!

  3. TeeJaw

    I’m a citizen firearm instructor. I conduct the following drill in my classes:

    At the 5-yard line, shooter stands facing down range with drawn pistol at the low ready position. Runner stands to shooter’s right facing opposite direction, with his right hand on shooter’s shoulder, and holding an object in his left hand, usually a hat or an empty ammo box. The runner decides when he will strart running, away from shooter in the opposite direction. Shooter is instructed that when he feels the runner’s hand leave his shoulder he is to raise the pistol to aimpoint and put two rounds into the target, accurately as he can.

    Runner is instructed to drop whatever he is holding in his hand when he hears the first shot, and to keep running until he hears the second shot, at which point he is to stop and hold right there. Then we measure the distance from firing line to the dropped hat and to the spot where runner stopped.

    Distance to dropped object is usually between 17-20 feet, distance to where runner stopped is usually 24-30 feet.

    Dennis Tueller has often said, “It’s not a 21-foot rule. It’s a drill to show that the bad guy with a knife can present a lethal threat at a greater distance than you might think.” It’s also a rule to contradict journalists and reporters who like to say the cop didn’t need to shoot the guy because he only had a knife and he wasn’t even close to the cop.

    • albundy57

      Marines do the same drill with enemy dead within one step. At least when rules of combat dont require determining intent, religion, sex, age of target. Obama!

  4. Matthew W

    Very interesting information to continue the officer safety discussion.

    Be Safe Blue !!

  5. Marty Johnson

    They need to CHANGE the legal standard from a subjective “I feared for my life” to an objective standard, “would an ordinary citizen feel threatened under the circumstances?” Every cop has learned the magic phrase “I feared for my life” as a talisman to protect him or her from suffering the consequences of a bad decision. And too many moronic citizens believe the survivor (the cop) when the deceased is not around to tell his side. An average citizen, without the same training, weapon and bullet proof vest does not get to be excused if they subjectively “feared for their life” but rather will lose if it was unreasonable under the circumstances for them to have shot someone.

    • TeeJaw

      It’s an objective reasonable standard in every state. Same for cops and citizens. Question is always the same, “What would a hypothetical reasonably prudent person (or a reasonable cop) have done or believed under the same or similar circumstances?” A subjective belief is usuallly also necessary, but a subjective belief alone won’t satisfy.

  6. Jesse James

    So if the officer already has his weapon drawn and at the low ready or even pointed at the suspect, how many feet MORE should he allow the suspect to advance before firing? lol I don’t understand the argument here at all. I don’t care about the 21 foot rule, I care about my life and if he is 35 feet from me when I shoot him, who the hell cares if he is charging at me with a knife?

  7. Rocky warren

    I attended LETC 93 in Park City, Utah and spoke with (then Sgt.) Dennis Tueller about the genesis of the “21 foot rule.”
    I wasn’t satisfied and determined to directly test the theory. My teaching partner Lt. Dave Rose and I performed the drill approximately forty times. Not only as a demonstration to Basic and Advanced Officers of “action vs. reaction,” but also as a stark example of the sheer lethality of edged weapon attacks.
    I would face a paper target at the rear of the range, while Dave faced a paper target at the live-fire line. Both our targets were a measured 21 feet away. Dave and I were shoulder, he facing front, me facing to the rear.
    Upon my first move running at the rear target, Dave was released to draw and fire on the front target. All holster security straps were in use as they would be on the street.
    There was not a single instance where Dave would not have been slashed or stabbed. We did the drill often enough, if Dave took a half-second too long, I’d use my “CIA Letter Opener” edged weapon to stab my target three or four times rapidly, then cut the target down to fall on the floor.
    Also of note in this exercise is the fact that there was no “uncertainty factor.” Dave KNEW he was responding to an edged weapon attack. Of the Officers I personally know who’ve been stabbed or slashed, only one ever saw the knife prior to being cut! And these knife assaults occurred under “low light conditions,” heightening the threat level even more.
    In my experience, and not holding this up as a scientific proof, but as repeatedly tested, 21 feet is clearly insufficient distance to eliminate or even attenuate an edged weapon threat!
    The Police Executive Research Forum guidelines about edged weapons hold no basis in fact and are actually, actively dangerous! I suggest they live up to their name and “research!” Their critique of the 21 foot rule is not justified nor realistic. Lessening of the 21 foot rule will only cause increased injury and even death to officers who hesitate even one-half second!

  8. Ron J. Brookshire Jr.

    It came from Indonesian and Filipino martial arts… Learned in villages with machetes vs armed soldiers by the resistance. Then filtered to military. Then to law enforcement.

  9. Sgt. Howard Freeman (Ret)

    While I was a firearms instructor with the Urbandale Police Department, the twenty-one foot rule came out. We ran our officers through it and to many surprises, the rule is valid. Officers found out they didn’t have the necessary reaction time to accurately defeat the threat.

  10. Bruce

    I once saw an episode of Myth Busters that demonstrated the 21 foot rule and showed how deadly edged weapons are on close quarters. We were trained to drop, roll on our backs, feet toward threat and fire between legs. Gave added time, legs for defense and more accurate shooting.

  11. Chief Mike Kovalyk

    I started as a firearms instructor for our department in 1982. I think I might still have the VHS tape of Tueller, I thought his first name was Dennis, but that’s here nor there. I used his exercise in our departments instruction as the usual maximum distance of our training drills was 21 feet. Back in the 80s most officers carried revolvers with a lot of old time holsters with the strap over snaps. The 21 feet I believe was that back then majority of shooting incidents was 21 feet and a lot of times less than that. rounds exchanged between both shooters was 3 to 4 and the shootings averaged 2-3 seconds. Now with the new generation of weapons,holsters those numbers have increased, but the Tueller rule is still one drill that I think should be at least mentioned especially as far as new officers with little or no firearms experience.

  12. Nick Wilson

    I’m sure many of us have done a version of this drill in trading, and can all attest to the seriousness of being caught off guard by a suspect with a knife. There is also an interesting Myth Busters episode that covers this topic, and includes a version with firearm at the ready vs a thrown knife.

  13. Alan Goldberg

    One of the things we need to do is stop calling this a It was merely a scientific experiment that demonstrated that 21 feet was the minimal distance to identify a threat, react, draw, fire and get out of the way of an individual armed with an edged weapon. It is not a RULE. It is one factor to consider in the deployment of deadly force. There are a plethora of other factors that need to be articulated before one reaches a point of objective reasonable action. Unfortunately, too many trainers and too many chiefs don’t understand it. Even when deadly force would permissible, the officer or agency just says that the suspect had a knife and the 21 foot rule was in effect. Articulation of the facts that allow a reasonable officer to make the decision to deploy deadly force need to be specific and clear.

  14. Greg Smith F41(r)

    Thank you for your article, it is interesting. I have been through this process, several times, without litigation. I worked with Lt. Tueller and was personally trained by him…

    I heard his voice (instructions) during my first shootout.

    For the record, his name is Dennis. There was no John Tueller on our Dept.

  15. Dennis Alexander

    Actually this distance has been modified to 35 feet.

  16. Matthew Carpenter

    The problem is that it has been misinterpreted as a “rule”. This is a “drill” to make officers aware of the dangers of edged weapons in close proximity. This is not a “rule” and should not be presented as such.


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