Personal Defense: Learn the Big 3 Checklist for the Use of Deadly Force

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Using firearms in self-defense, whether in the home or out in public, is deadly serious business. That’s why, as a society, we came up with rules governing the justifiable use of deadly force in the United States of America. The following rules, or what we call “The Big 3 Checklist” have been codified and affirmed by courts throughout the nation. 

Before we address the Big 3 Checklist for justifiable deadly force, we need first understand the legal definition of deadly force. This is the standard by which you will potentially be judged in the aftermath of a lethal force encounter where you were forced by circumstance to defend yourself with a firearm. 

Deadly force: “Deadly force is that force which causes, or is likely to cause, death or serious bodily harm.” 

The definition of death is easy to understand, it means assuming room temperature. However, what do they mean by “serious bodily harm”?  Legally, Serious Bodily Harm is “such harm that results or is likely to result in permanent disfigurement or require prolonged hospitalization and/or prolonged physical or mental rehabilitation.” 

From this definition of “Serious Bodily Harm” we can see that, although a baseball bat to the knees might not kill you, it certainly is likely to cause permanent disfigurement and require prolonged rehabilitation. Ergo, a baseball bat to the knees is Deadly Force. Rape and kidnapping require prolonged rehabilitation and mental health treatment. Both are felonies and both fall under the definition of deadly force. Deadly force puts the intended victim in fear for their life. 

Also, we must understand that the implied threat of deadly force IS deadly force. You are NOT legally required to wait for someone to shoot at you or stab you before you are legally allowed to use deadly force in self-defense. An attempted kidnapping or attempted rape IS deadly force and can be justifiably prevented with a deadly force tool. 

Less-than-Lethal force: “That force which is not likely to cause death or serious bodily harm.” 

Less-than-Lethal force tools are force options for dealing with threats that do not reach the level of deadly force or put us in fear for our lives. Law enforcement officers use less-than-lethal force tools to deal with threats that have not reached the deadly force level. The most common tools are OC (pepper spray), the TASER unit, and batons/nightsticks. 

Keep in mind, we do not attempt to use less-than-lethal tools to stop deadly force threats in an attempt to make ourselves appear to be “more reasonable”. You are NOT required to try to use less-than-lethal force tools prior to using deadly force. The amount of force you will use is determined by the threat you are facing. If the threat is deadly/lethal, then you are absolutely legally and morally justified in stopping that threat with a deadly force tool.  

Disparity of Force: Consider the age, sex, size, number and skill level, as well as weapons possessed by attacker(s) versus victim. In regards to a disparity or demonstrable difference, the courts recognize that if the attacker has disparity in their favor (Size, Strength, Age, Sex, Number) the defender may use more force than might otherwise be needed.

A grown man attacking a small child is a gross disparity of force situation. Even though no weapon may be present, an adult attacking a small child represents a deadly force threat. A man, even with no weapon present, attempting to kidnap a child is a deadly force attack. 

Additionally, the courts have ruled that if two or more persons attack a single defender, the strength in their numbers constitutes a threat of lethal or deadly force, regardless of whether or not the multiple attackers show weapons. The courts recognize that a lone defender can be crippled or killed if they are attacked by multiple persons, therefore, the single defender can be legally justified in using deadly force to stop the attack.

Another common disparity of force situation would be a young, physically fit male attacker, in their late teens or early twenties, assaulting an older man or woman. The courts do not expect a 65 year old man with a history of back problems to duke it out toe to toe with a young, fit attacker. In such a case, the 65 year old man would be legally justified in using greater force than if the two parties’ age and strength were more closely matched. A single person is not expected to take on three gangbangers like Jackie Chan or Jason Statham. 

The Big 3 Checklist

Before you can legally, and morally, use deadly force, you must swiftly address what has come to be known as “The Big 3 Checklist”. This list includes; ability, opportunity, and intent. All three must be present for deadly force to be justified.


Ability might seem simple. Did the attacker(s) have the ability to cause deadly force to the defender? The presence of a weapon is an obvious answer; gun, knife, claw hammer, steel pipe, baseball bat, etc. all present the ability to do deadly harm to a defender. 


Did the attacker have the opportunity to exercise deadly force against the defender? Once more, this might seem simplistic, but we need to address it. If your angry neighbor is standing on the other side of a chain link fence holding a baseball bat, calling you everything but Christian and intelligent, is he a deadly force threat? He has a weapon and is demonstrating the intent to harm you, but does he have the opportunity? In this situation, no he does not. 

If your angry neighbor threatens you with a shotgun from the other side of the fence, that is a different story. What if your neighbor, armed with a bat, crosses the fence and follows you up to your porch? Now the situation has changed. The attacker took steps to give himself the opportunity to harm you, plus he is armed and has already made threats. 

How about the abusive ex-husband, drunk, screaming and pounding on a locked door? Intent; yes. Ability; yes. Opportunity, not yet. Despite what Joe Biden said, you cannot legally point a shotgun at the door and fire two blasts. However, if an abusive ex-husband kicks in the door in order to give himself the opportunity, all three questions have been answered: ability, opportunity and intent. 


Intent is the big one. Just because someone has a weapon and is near you does not justify deadly force. Let’s say you stop at a fueling station to fill up your car with gas. You walk into the station and there is a man in a blue uniform filling up his coffee cup. He has a pistol and he is near you. Is he a deadly force threat? Of course not. The same would apply to a citizen lawfully carrying a handgun that you might be able to see. Without intent, there is no deadly force. 

Intent can be verbal; “Give me your wallet or I’ll kill you.” or “F*@k you you piece of sh*t I’m gonna smash your head in”, going back to the angry neighbor scenario. These are verbal threats of deadly force.

However, as often as not, intent is non-verbal. If you approach your car and a man quickly moves between you and the vehicle and produces a knife, gun, etc. that is demonstration of intent, even if he doesn’t say a word. 

If someone forcibly or stealthily (cut through a screen door) enters your home, that is demonstrated intent. If a person attempts to stop you from going about your way, grabs you on the street, blocks you from getting to your car, blocks your exit from a building, whatever, that is demonstrated intent, even though no words were spoken. If a person, though apparently unarmed, attempts to take YOUR gun, that is demonstrated intent of deadly force. Remember, if an attacker takes your gun they will either kill you or an innocent person. That is reality and that is deadly force.  

This would seem like an opportune moment to remind you that it is your responsibility while carrying a firearm in public to keep that gun out of the hands of others. You must make the mental commitment, right now, that you will never allow yourself to be disarmed. If an attacker takes your gun, they will most certainly attempt to kill you with it and/or they will attempt to kill other innocent people. These innocent people might just be your family members, your loved ones. Remember, this is deadly serious business and must be approached as such.


This is an excerpt from Paul Markel’s book, Living Armed: Understanding Guns for Home Defense and Concealed Carry. Paul G. Markel is the founder of Student of the Gun University and has been teaching Small Arms & Tactics to military personnel, police officers, and citizens for over three decades. He is the author of numerous books and is a combat decorated United States Marine veteran.

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