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Departments : The Winning Edge

Revisiting the "21-Foot Rule"

The Tueller Drill is often evoked as justification by officers after a shooting…But is it scientifically defensible?

September 18, 2014  |  by Ron Martinelli

Photo: Martinelli & Associates
Photo: Martinelli & Associates

For decades now many American officers have heard use-of-force instructors discuss the "21-Foot Rule" during officer safety, firearms, and deadly force training. As a use-of-force instructor and a practicing forensic police practices expert, I have also trained and testified to this concept myself.

The 21-foot rule was developed by Lt. John Tueller, a firearms instructor with the Salt Lake City Police Department. Back in 1983, Tueller 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 him.

After repeating the drill numerous times, Tueller—who is now retired—wrote an article saying it was entirely possible for a suspect armed with an edged weapon to fatally engage an officer armed with a handgun within a distance of 21 feet. The so-called "21-Foot Rule" was born and soon spread throughout the law enforcement community.

But is the "21-Foot Rule" a forensic fact or a police myth?

Reactionary Gap

Tueller designed his firearms action-reaction experiment as a training device to help his students better understand 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. The closer an assailant is to an officer, the less time an officer has to defensively react to any aggressive action the assailant makes.

Tueller has said in video interviews 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 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 an officer-involved shooting case where an officer with a carbine shot and killed a suspect armed with a knife from a distance of more than 150 feet and attempted to use the "Tueller Drill" as his defense.

Instructors and experts also seem to have forgotten that the original scenario of Lt. Tueller's drill 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 officers already had their guns out of their holsters and were either at the "low ready" position or directly aimed at the suspects who were either armed with knives or furtively reaching into their waistbands.

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.

The Variables

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

When an officer experiences a threat, it takes on average .58 seconds to experience the threat and determine if it is real. It then takes on average .56 to 1.0 seconds to make a response decision. Humans have five possible responses to threat: 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 uses 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 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). 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—Several factors affect an officer's survival against an attacker. For instance, an officer or detective whose sidearm is secured in a Level III holster will certainly have a slower draw-to-target acquisition time than an officer drawing from a Level I holster. An officer's experience and competency with his or her holster system and combat shooting style are also critical human factors in that 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 and 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.

Perception lag—Once the average officer gets on target, it takes him or her .56 seconds to make a decision to commence shooting. However, it then takes that same officer .25 to .31/100ths of a second per trigger pull to fire. As the deadly force scenario rapidly evolves, it takes that same officer on average .5 to .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."

The reason why some suspects are found to have entry wounds in their sides and backs when the officers who shot them say the suspects were facing them when they fired is often the perception action-reaction lag time and the manner in which information was processed by the officers' brains. This is pretty sophisticated information for a criminal or civil jury to understand and consider.

Fantasy or Forensic Fact

The fields of contemporary police practices and applied sciences are rapidly changing. Applied science, by its nature, supports or rejects hypotheses 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 and 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.

Whether the "21-Foot Rule" is an applicable defense in an officer-involved shooting actually depends upon the facts and evidence of each case. The shooting of a knife-wielding suspect at less than 21 feet by an experienced, competent, and well-equipped officer who has the tactical advantage of an obstruction such as a police vehicle between herself and her attacker might be inappropriate. But the shooting of a knife-wielding assailant at more than 21 feet by an inexperienced officer, wearing a difficult holster system, with no obstructions between herself and the attacker might be justified.

As the 1989 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.

Note: The author would like to thank forensic expert team members Homicide Lt. Bob Prevot (Ret.), M.A., ballistic scientist/firearms expert Lance Martini, M.S., firearms expert Larry Nichols, and NSW operational psychologist and psychiatry professor Douglas Johnson, Ph.D., for reviewing and contributing to this article.

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.

Related Video:


  1. The Tueller Drill, Video Interview with Lt. Dennis Tueller (Ret), GunWebsites,, 03-25-11
  2. How Close Is Too Close? (Article) Tueller, Dennis, SWAT Magazine, 03-1983
  3. Understanding & Leveraging the Psychophysiology of Emotional Intensity, Sztajnkrycer, Matthew, M.D., Ph.D., Force Science Institute®, Minnesota State University, Presentation at San Jose (CA) Police Department, 02-08-10
  4. Ibid.
  5. Processing Under Pressure: Stress, Memory and Decision Making in Law Enforcement, Sharps, Matthew, Ph.D., © 2010, Loose Leaf Publishing, Flushing, N.Y.
  6. Some fundamental of Human Performance: Applications to Police Activities, Schmidt, Richard, Ph.D., Force Science Institute®, Minnesota State University, Presentation at San Jose (CA) Police Department, 02-09-10
  7. Violent Encounters – A Study of Felonious Assaults on Our Nation’s Law Enforcement Officers, U.S. Department of Justice, Federal Bureau of Investigations, Publication #0383, 2006
  8. Reaction Times in Lethal Force Encounters, The Tempe Study, (Article) Lewinski, Bill, Ph.D., Hudson, Bill, Ph.D., The Police Magazine, Sept/Oct., 2003, pp. 26 - 29
  9. The Psychology and Physiology of Deadly Conflict in War and in Peace, Grossman, D.A., PPCT Research Publications, 2004
  10. Deadly Force Encounters: What Cops Need to Know to Mentally and Physically Prepare for and Survive A Gunfight, Artwhol, A, Christensen, L, Paladin Press, 1997
  11. Sharpening the Warrior’s Edge: The Psychology & Science of Training, PPCT Research Publications, 1995
  12. Motor Learning and Performance, Schmidt, R.A. and Wrisberg, C.A., 3rd Edition, Human Kinetics Publishers, 2004
  13. Human Perception and Performance, (Article) Keetch, K.M., Schmidt, R.A., & Young, D.E., Journal of Experimental Psychology, 2005, No. 31, 970-978

Comments (31)

Displaying 1 - 31 of 31

John F. Tilley @ 9/20/2014 9:58 AM

The author makes no mention of the Calibre Press video "Surviving Edged Weapons" that came out in 1988...over an hour in length it continued the application of the "21' rule" and was instrumental in spreading it.

Carlos @ 9/20/2014 10:03 AM

People must understand that Tueller's 21-foot rule was meant to be a guideline; nothing more than a starting point. This distance changes based on a lot of variables such as the fitness level of the attacker, the mental state of both attacker and Officer, the level of training of both participants, the terrain of the encounter, the weather, ambient light, etc.

Each Officer should be given the opportunity what their safe distance is based on multiple executions of the "Tueller Drill" in as many different terrains and against as many different "attackers" they can. It is important to conduct this exercise while using their actual duty gear and while in full uniform.

I used to run this exercise as regularly as I am able against different opponents. In full duty uniform, it seems my safe distance is closer to 23-feet, 25-feet if I am wearing winter gear (jacket and gloves). JM2CW.

rob @ 9/20/2014 10:54 AM

Each situation is different, a suspect within 21feet who is armed presents a clear danger but any armed suspect is dangerous. There are always variables that come into play and distance is not the only one to be considered. I am curious if the writer has ever faced a deadly force encounter or does reviewing others use of force make him a "expert".

BigErn @ 9/20/2014 2:52 PM

The article fails to mention anything about the officer having a clipboard or anything else in his hands at the time. Also you have to take into consideration the assailants momentum. Anyone who thinks the suspect is going to be "knocked down" and instantly stop when shot has never been in a close combat firefight. With the use of pain killing street drugs like cocain and methamphetamine the ability of quickly stopping an attacker is greatly reduced, increasing the 21 foot rule distance.

Deborah Siefer @ 9/20/2014 3:43 PM

I can attest To the 21 foot rule. In practice I kept saying to the assailant put your weapon down put your weapon down. I like the assailant come within about 10 feet me. Still ordering him to put his weapon down, he struck me with his 6 foot rod. Striking my hand. Not enough to knock the fireman from my hand. But at that point I shot as well. Shooting center mass. Killing assailant. Had it been a real situation. I will not let an assailant get that close again. If he / she doesn't put weapon down as ordered. I was trying to get the assailant to comply to my order in which he didn't. Therefore, you need that distance when there is another weapon involved and it is not that of another officer's; but the assailant. You can't have less distance and have chance to pull a weapon if the assailant rums towards you with a rod, stick of length or weapon as it was used like in my practice. There was just not enough time. Believe me I am one for no violence. I will give you a chance. But when it comes to a deadly weapon whether it's a steel rod, two by four or a gun. It's the assailant or me; it's going to be me or I am going down fighting.

TheRookie @ 9/20/2014 10:15 PM

Agree with Carlos & Many here. I personally know the 21 foot or any other distance rule. I was put on paid medical administration leave on June 15, 2008 @ 0239hrs. I was retired by mandate in December 2010. It started at approx. 31 feet & ended with hands on with a tweaked out crack-head trying to strip my duty weapon to kill me. That after a full can of 15% oleoresin capsicum Pepper Spray, numerous strikes, & close combat use-of-force. He won the battle, but not the war. I ended with a torn out left knee, gouged eyes, & left forearm torn open that got severely infected. All at age of 48. Have always Monday morning QB'd myself. Should have shot him, but I'd have been put in Officer Wilson's shoes, too. Damned if you do. Damned if you don't.

TX Lawman @ 9/22/2014 6:24 AM

I don't what closet Ron Martinelli has been living in but there have been multiple studies done on reactionary gap and it has been expanded to 30 feet. Too many officers were getting injured at the 21 feet mark. More studies were conducted and the gap has now been moved to 30 feet with plenty of evidence to support it. Texas courts accept the new 30 foot gap as justification to use deadly force.

Pup @ 9/22/2014 9:40 AM

>Rookie, sorry to hear it happen to you. As for the estimated rule, I feel it depends on the mindset of the officer. As myself, I had a suspect run out of the house with a knife towards me yelling to kill him. I was standing in the "V" of my car door, weapon out. When the suspect got to the front of my radio car, I gave commands in a certain language. Mindset, I didn't feel threaten at the time. Could have I killed him legally, as he was within 10', Yes. But, his actions lead me to believe he didn't want to die. Plus, I felt I had enough cover and time to engage, if he went beyond the bumper. The suspect stopped and went to other deputies, who used the bean bag. I question myself if I did the right thing. The Lt. said it was my years of experience and being a tactical instructor which lead me to make the right decision. What do you think?

B. Sato @ 9/23/2014 10:32 AM

Hey PUP you absolutely did the right thing brother. You are the one who has to live with your actions. You saved someone's life, a father, a son, a human being. I went through a similar experience and am glad that I didn't take his life. I also take Krav Maga, its great for striking and disorienting a suspect, giving you time to get to your weapon or to handcuff the suspect. I took the ASP handcuff Trainers class, and speed cuffing will often prevent a fight before it starts. I highly recommend both. Get out there and train Brothers and Sisters.

Civilian @ 10/12/2014 10:51 PM

I agree with you Pup. I don't think there is a reason to kill a man if you really don't have to

Ron Martinelli @ 10/15/2014 3:20 PM

While I believe that I have been pretty clear with what I've opined on in my article, some times the message needs to be repeated so it's context is understood and appreciated officer safety-wise and in a court of law. As one who investigates, analyzes and testifies on OISs for a living, I can assure you that the vast majority of officers still quote the "21 Foot Rule" in depositions and in court. The number of feet an officer is from a potentially deadly assailant is not necessarily the point. It is a consideration of "totality of circumstances" which are incredibly varied. As we firearms and use of force instructors understand, the quality of instruction, instructor experience and officer competency varies from region to region and from department to department. Officers, attorneys and jurors who don't understand this and assume that officers all receive the same training and have the same understanding are those who "live in closets." Our research hopes to change this paradigm.

Retired @ 10/20/2014 6:16 PM

Great article. I believe the word should be should be "auditory exclusion" not "occlusion".

Semper Fi

Richard @ 1/2/2015 8:10 AM

Great point Ron. It is always the "totality of circumstance" and I always viewed the 21' rule, not as a rule, but a great training point teaching new Officers the deadly effects that can happen and to be prepared. Most newbies are amazed at going through that drill and finding they are "stabbed" before they can draw, present & fire their weapon. I tend to agree that even 30' is not always a safe distance from a subject with a weapon if your own weapon is holstered.

TX Lawman @ 1/5/2015 6:25 AM

The 21 foot rule was tossed out many years ago and the 30 foot rule has been in place since then, at least in Texas. Their has been many studies on the 30 foot rule and it is defendable in our courts. Stay safe!

hmbval @ 1/9/2015 4:22 PM

To Tex Lawman: Dr. Martinelli was actually agreeing with you. I'm not sure where the negative comment came from. You might want to read Graham vs. Connor to find out what "reasonably objective is all about.

W. Mazur @ 2/20/2015 9:23 AM

Article underscores the many variables that affect the individual officer's decision making process as it relates to the "Reactionary Gap". Dr. Bill Lewinski of Force Science Institute has spearheaded research on this exact topic that is worth reading. I urge you to look at his studies.
NOTE: the Reactionary Gap for physical assault (hands, feet) is much closer, as we all know, and gets cops killed at an alarming rate...the "Unarmed Man Myth"...yet all you hear is "Officer shoots unarmed man". This is an equally important topic...
Be safe, stay vigilant.

diosdado apias @ 8/1/2015 11:24 PM

I think the "21 foot rule" is misnomere if this has basis with the Tueller drill that uses 21 feet as a feasible reactionary gap. This should not be use as a rule like a substantial law as in self defense in the penal code that if you committed it as long as you are within the elements of self defense you will be justified. The Tueller drill is not a doctrine that it can be universally true to become a law. it is a theory back up by experiment to determine if within a certain distance one can still react to defend himself against a rush-up assault. the 21 feet used by Tueller as a reactionary gap shows only that at a certain distance or gap one can still react or too late to react to be able to defend himself from attack.

@ 10/21/2015 9:35 AM

These are all great scenarios that invoke extremely critical thought. My first time ever hearing of "The 21' Rule" was 4 years ago in my CCW class. While I believe it's a helpful reference tool, I also understand that it can be a bit trivial under various circumstances. I've been exposed to some very insightful information on this blog. Thank all of you for your input😉

Ken b @ 12/14/2015 10:13 PM

All things lead to training. The issue is not distance it the reaction time. Let's face reality there are sport shooters that practice drawing weapons daily. Police are required min hours per year for life and death situations. All rules and use of force issues can be completely revisited when the realization of extreme lack of training is addressed

Ukimok @ 12/19/2015 6:30 AM

This is all great analysis but I am afraid it has little to do with the problems currently plaguing law enforcment. The issue is more about decision making in general and situational awareness training at a larger scale. How many feet at which you draw a weapon is less important than having the tact or skill to diffuse or avoid a bad situation in the first place. This requires a higher level of professionalism but has a great impact on lives saved on both sides of the weapon.

BillCa @ 12/21/2015 10:48 PM

Another resource for use-of-force dynamics and scientific analysis is The Force Science Institute ( Based at Minnesota State University-Mankato they use sophisticated time-and-motion measurements to document-for the first time-critical hidden truths about the physical and mental dynamics of life-threatening events, particularly officer-involved shootings.

Recent articles can be found at

Glenn @ 8/31/2016 12:27 PM

It's *Dennis* Tueller, not John Tueller.

James Green @ 10/30/2016 12:20 PM

This is an interesting read. Police need to keep in mind also, that "innocent subjects" have a right to self defense against any enimy, foreign or domestic. The police in America are domestic terrorists and should be delt with in such a matter.

mark @ 11/29/2016 5:59 PM

My dad, who was in Korean War told me he had a 50 foot rule!!!

Chip DeBlock @ 12/22/2016 4:15 PM

We decided to discuss this story on the LEO Round Table law enforcement talk show. Here's a link to the episode in case you want to check it out:

Chip DeBlock @ 12/22/2016 4:16 PM

We decided to discuss this story on the LEO Round Table law enforcement talk show. Here's a link to the episode in case you want to check it out:

Jon Seeger @ 3/22/2018 6:14 AM

My son went to academy in Ohio. He was told change to 15 ft. Not sure what is the rule. U have safety catches on holsters now. Kids can run faster. There is a case in Odanah,WI. Had that happen. People are arguing. The parents are going for wrongful death. 7 mill. U might check this out for your article

Fyl @ 9/15/2018 12:47 PM

Don't forget to apply it to "fit, known or probable trained and dangerous" types, as in the training exercise it stems from

Special Forces veteran or murder suspect, yay; aggitated middle schooler or grandma, nay.

DeusExMachin @ 10/7/2018 8:36 PM

There is no such thing as the 21 ft Rule. The Tueller DRILL, devised by Sergeant Dennis Tueller, of the Salt Lake City, Utah Police Department, was NEVER intended to be a rule, and using it to justify deadly force inside some arbitrary distance and to justify complacency outside is has no basis in fact, and is diametrically opposite of what Tueller was trying to convey.
Tueller, himself, is quite vocal about this fact.

MarcB60 @ 10/15/2018 2:27 AM

Please clarify something for me. I know the answer, have many in family [past on] who were Blue. But some 'Individual' I know claimed that Fire Arms training for officers included; After an officer fires the first round at a suspected threat, he is obligated, no, REQUIRED, to EMPTY his weapon at the threat? I have never heard of such a rule, nor aspect to weapons training.

Joe @ 11/2/2018 12:14 PM

Excellent article, as usual. I recently forwarded your post about worship places safety and security to a local temple. I think it may have moved them off square one on their security continuum. At least they contacted me to help them think things through. I'm not a pro in this area but will try to move them in the direction of improving their situation.

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