Defense of Others in Criminal Law

Defense of Others

When a person uses force to protect someone else from an unlawful attack, criminal law may recognize that conduct as justified. This defense is known as defense of others.

The basic idea is straightforward: the law does not necessarily require a person to stand by while another human being is subjected to unlawful violence. Under appropriate circumstances, a person may intervene and use reasonable force to protect a third party.

Cornell Legal Information Institute — Defense of Others

But the defense has limits. A person who intervenes cannot automatically use whatever force he or she considers appropriate. The force generally must be reasonably necessary to protect the other person from the threatened harm. The precise rules vary among jurisdictions.

What Is Defense of Others?

Defense of others is a criminal defense that permits a person to use reasonable force to protect a third party from an unlawful threat of force.

For example, suppose Alex sees Jordan attacking Sam with a knife. Alex tackles Jordan and strikes Jordan to stop the attack.

Ordinarily, intentionally striking another person could constitute a crime. But if Alex reasonably believed that Sam faced an imminent threat of serious physical harm and used proportionate force to stop the attack, Alex may be entitled to claim defense of others.

The doctrine therefore operates as a justification defense. The argument is not necessarily that Alex did not commit the physical act. Rather, the argument is that the act was legally justified under the circumstances.

Cornell Legal Information Institute — Criminal Law: Defenses

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The Relationship Between Defense of Others and Self-Defense

Defense of others is closely related to self-defense.

Self-defense concerns the protection of oneself from unlawful force. Defense of others extends the same basic principle to the protection of another person.

Consider the difference:

• Self-defense: “I used force because I reasonably believed I was being attacked.”
• Defense of others: “I used force because I reasonably believed another person was being attacked.”

Both doctrines are concerned with the same fundamental question:

Was the use of force reasonably necessary to prevent unlawful harm?

The difference is the person being protected.

Self-defense generally protects the defendant’s own physical security. Defense of others protects the physical security of another person.

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Why Does Criminal Law Recognize Defense of Others?

Criminal law generally prohibits individuals from intentionally using force against other people. But criminal law also recognizes that there are circumstances in which using force is not wrongful.

If an attacker is strangling another person, for example, the law may recognize that intervening to stop the attack serves an important social interest.

Defense of others reflects several principles.

1. Protection of human life

The law has a strong interest in preventing serious physical harm and death.

2. Prevention of unlawful violence

An individual may sometimes intervene when another person is unlawfully attacking someone.

3. Recognition of justified force

Not every intentional use of force is criminal. Circumstances can transform otherwise unlawful conduct into justified conduct.

4. Protection of third parties

The law does not necessarily treat a person as a passive observer when another person is facing imminent unlawful violence.

The defense therefore represents an important boundary between violence as criminal conduct and force as a legally justified response to violence.

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The Basic Elements of Defense of Others

Although the precise formulation varies by jurisdiction, a defense-of-others claim commonly involves several questions.

1. Was the third person facing unlawful force?

The first question is whether the person being protected was actually threatened with unlawful force.

For example, if someone is deliberately attacking another person, the circumstances may support defense of others.

But if the defendant intervenes in a lawful use of force, the justification may not apply.

The underlying conduct therefore matters.

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2. Was the threat imminent?

Defense of others generally concerns an immediate or imminent threat rather than a speculative future danger.

For example:

“I thought this person might attack my friend someday.”

is very different from:

“I saw the person holding my friend down and repeatedly striking him.”

The closer the threat is to immediate physical harm, the stronger the justification may be.

A person generally cannot use force today merely because another person might pose a danger tomorrow.

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3. Did the defendant reasonably believe intervention was necessary?

This is one of the central questions in defense-of-others cases.

The defendant’s belief is important, but the law generally does not treat every subjective belief as sufficient.

The question may be whether the defendant reasonably believed that intervention was necessary to protect the third person.

Consider this example.

A man sees two people arguing loudly. One raises his hand but does not actually attack the other. The observer immediately tackles him and seriously injures him.

The observer may claim that he believed an attack was imminent. But a court may ask whether that belief was reasonable under the circumstances.

The defense therefore often involves both:

• the defendant’s actual belief; and
• the objective reasonableness of that belief.

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4. Was the force reasonable?

Even when intervention is justified, the amount of force used generally matters.

A person may be justified in using force to stop an attack without being justified in using unlimited force.

For example, suppose a person pushes another person away from someone being punched. If the attacker falls and the danger ends, continuing to beat the attacker may no longer be justified.

The legal question can therefore change during the incident.

At one moment:

Force may be necessary.

A few seconds later:

The threat may have ended.

The justification generally depends on the circumstances existing when the force was used.

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Proportionality and Defense of Others

One of the most important limitations on defense of others is proportionality.

The response generally must correspond reasonably to the seriousness of the threat.

This does not necessarily mean that the defender must use exactly the same amount of force as the attacker.

If someone is attempting to cause deadly harm, the defender may potentially use force capable of preventing that deadly harm.

For example, if an attacker is attempting to stab another person, the defender may potentially use substantial force to stop the attack.

By contrast, responding to a minor shove with potentially deadly force presents a much more difficult justification.

The key question is not mathematical equality.

It is whether the force was reasonably necessary under the circumstances.

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Deadly Force in Defense of Others

The most serious questions arise when the defendant uses deadly force.

Deadly force is force that is intended or likely to cause death or serious bodily injury.

Generally, deadly force is subject to stricter requirements than ordinary nondeadly force.

A person who intervenes on behalf of another ordinarily must have a sufficiently serious justification for using deadly force.

For example:

David sees an attacker pointing a firearm at Michael. David shoots the attacker to stop the attack.

That case presents a substantially different justification question from:

David sees someone slap Michael once and responds with deadly force.

The seriousness and immediacy of the threatened harm are central.

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Must the Third Person Actually Be Innocent?

This question becomes particularly complicated when the person being protected was not completely innocent.

Suppose a police officer lawfully uses force against a suspect. A bystander incorrectly believes that the officer is unlawfully attacking the suspect and intervenes.

Can the bystander claim defense of others?

The answer depends on the jurisdiction and the applicable doctrine.

The law must determine whether the circumstances actually justified intervention or whether the defendant’s mistake was legally excusable.

This illustrates an important point:

Defense of others is not simply a license to intervene whenever a person appears to be in danger.

The surrounding legal circumstances matter.

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Reasonable Mistake and Defense of Others

A particularly important issue is the defendant’s mistake about the circumstances.

Imagine that Alex sees Chris reach into a jacket while confronting Dana.

Alex believes Chris is reaching for a gun and attacks Chris to protect Dana.

Chris was actually reaching for a mobile phone.

Alex was mistaken.

The legal question becomes whether Alex’s belief that Dana faced an imminent threat was reasonable.

Jurisdictions differ in how they formulate the precise rule. Some approaches focus heavily on the reasonableness of the defendant’s belief. Others may distinguish between situations in which the person being defended would have been entitled to use self-defense and situations in which the defendant mistakenly believed that such a right existed.

The distinction can become extremely important in close cases.

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The Traditional “Alter Ego” Approach

Historically, some jurisdictions followed what is often described as the alter ego approach.

Under this theory, a person defending another generally “stands in the shoes” of the person being defended.

If the third person would not have been entitled to use self-defense, the intervener might also lose the defense.

For example, if the person being protected was actually the aggressor, the traditional approach could make it difficult for the intervener to claim justification.

This approach reflects a relatively strict principle:

A defender should not acquire a greater justification than the person being defended possessed.

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The Modern Reasonable-Belief Approach

Many jurisdictions have moved toward a more flexible approach based on the defender’s reasonable perception of the circumstances.

Under this approach, the central question may be whether the defendant reasonably believed that the third person was in imminent danger and that intervention was necessary.

Cornell’s Legal Information Institute notes that most jurisdictions do not require a special relationship between the defender and the person protected, although some jurisdictions may impose such a requirement.

This approach recognizes the practical reality of emergencies.

A person witnessing a violent confrontation may have only seconds to decide what is happening. The law may therefore evaluate the decision in light of the circumstances as reasonably perceived at the time rather than with perfect hindsight.

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Is a Special Relationship Required?

Generally, defense of others does not require the defendant to have a special relationship with the person being protected.

A person may potentially intervene to protect:

• a spouse;
• a child;
• a parent;
• a friend;
• a stranger;
• a coworker; or
• another member of the public.

However, jurisdictions differ.

Some jurisdictions historically required or recognized special relationships in particular circumstances. Others permit intervention whenever the legal requirements for defense of others are satisfied.

Therefore, the existence of a family or personal relationship is not universally required.

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Defense of Others and Police Officers

Defense of others can overlap with the lawful use of force by police officers.

Police officers may have statutory or common-law authority to use force under particular circumstances. A private citizen intervening to protect another person must be careful not to assume that every police use of force is unlawful.

For example, an officer may lawfully restrain a suspect.

A bystander who misunderstands the situation may believe the suspect is being assaulted and attempt to intervene.

Whether the bystander can invoke defense of others will depend on the applicable jurisdiction and the actual circumstances.

This demonstrates why the defense requires more than simply identifying one person as the apparent victim.

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Defense of Others and Defense of Property

Defense of others should also be distinguished from defense of property.

Defense of others protects a person from unlawful physical harm.

Defense of property concerns the protection of property interests.

The distinction can matter because the law generally places greater restrictions on the use of force to protect property than on the use of force to protect human life.

For example:

A person uses force to stop an attacker from seriously injuring another person.

This is a classic defense-of-others situation.

By contrast:

A person uses force to prevent someone from stealing a bicycle.

That is principally a property-defense question.

The seriousness of the threatened harm is therefore critical.

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Defense of Others and Necessity

Defense of others can also be distinguished from the necessity defense.

Necessity generally concerns conduct undertaken to avoid a greater harm under circumstances recognized by law.

Defense of others is more specifically concerned with the use of force to protect another person from unlawful force.

The doctrines may sometimes overlap factually, but they rest on different legal principles.

Defense of others is essentially a form of protective justification.

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A Practical Example

Consider the following scenario.

Emma is walking through a parking lot when she sees an attacker holding another person, Daniel, against a vehicle.

The attacker is repeatedly striking Daniel.

Emma reasonably believes Daniel is in immediate danger of serious physical injury. She pushes the attacker away and holds him on the ground until the danger ends.

Emma is later charged with assault.

Her defense may be based on defense of others.

A court could examine:

1. Whether Daniel was actually facing unlawful force.
2. Whether Emma reasonably believed Daniel was in immediate danger.
3. Whether intervention was reasonably necessary.
4. Whether Emma’s force was proportionate to the threat.
5. Whether Emma stopped using force when the danger ended.

If the evidence supports these conclusions, Emma may have a valid justification defense.

Now change the facts.

The attacker has already stopped, Daniel has walked away, and the attacker is lying on the ground.

Emma then repeatedly kicks the attacker.

The justification becomes much weaker because the immediate danger may have ended.

The same person may therefore be justified in using force during one stage of an encounter and unjustified in using force later.

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Defense of Others Is Not a License for Vigilantism

An important limitation is that defense of others should not be confused with private punishment.

The purpose of the defense is protection, not retaliation.

A person may potentially use force to stop an attack.

That does not necessarily mean the person may:

• chase the attacker after the danger has ended;
• punish the attacker;
• inflict unnecessary injuries;
• continue using force after the threat disappears; or
• impose personal justice.

The distinction can be expressed simply:

Protection is different from revenge.

Once the immediate justification disappears, continued violence may become criminal.

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The Role of Hindsight

Courts evaluating defense-of-others claims face a difficult problem.

The defendant may have had only seconds to act, while the court may have months or years to examine the incident.

That creates the danger of hindsight bias.

A judge or jury knows what ultimately happened. The defendant did not.

Suppose a person sees another individual raise a firearm and immediately intervenes. The weapon later turns out to have been unloaded.

The relevant question cannot necessarily be reduced to:

“Was the gun actually loaded?”

The circumstances surrounding the defendant’s perception may be crucial.

The law of justification therefore often asks what the defendant reasonably perceived at the time rather than simply what became known afterward.

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Evidence in Defense-of-Others Cases

Evidence can be particularly important because justification often depends on the circumstances as they existed at the moment of intervention.

Relevant evidence may include:

• eyewitness testimony;
• surveillance video;
• photographs;
• medical records;
• physical injuries;
• communications between the parties;
• statements made during the incident;
• weapon evidence;
• forensic evidence; and
• the relative positions of the people involved.

Video evidence can be especially significant because it may show whether the threat was continuing, whether the defendant had other reasonable options, and when the use of force began and ended.

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Who Has the Burden?

The allocation of burdens concerning affirmative defenses varies by jurisdiction.

The prosecution generally bears the fundamental burden of proving the elements of the charged crime beyond a reasonable doubt.

The treatment of a justification defense, however, can differ depending on state law. Some jurisdictions place a burden of production on the defendant and then require the prosecution to disprove the justification beyond a reasonable doubt once properly raised. Other jurisdictions formulate the allocation differently.

This is one reason criminal defenses must always be analyzed under the law of the particular jurisdiction.

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Defense of Others as a Justification Defense

Defense of others is generally classified as a justification defense.

That distinction is important.

A justification defense essentially argues:

“The conduct was socially and legally permissible under the circumstances.”

This differs from an excuse defense.

An excuse generally accepts that the conduct was wrongful but argues that the defendant should not be held criminally responsible because of the defendant’s circumstances or condition.

Defense of others belongs primarily to the first category.

The defendant is not necessarily saying:

“I committed the crime but should be forgiven.”

The argument is:

“The use of force was justified because I was protecting another person from unlawful harm.”

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Defense of Others and Criminal Responsibility

Defense of others illustrates an important principle of criminal law: criminal responsibility depends not only on what a person does, but also on why and under what circumstances the person acts.

Two people may perform the same physical act but have radically different legal positions.

Consider two people who strike an attacker.

The first strikes the attacker because he wants revenge after an argument.

The second strikes the attacker because the attacker is attempting to kill another person.

The physical act may look similar.

The legal meaning may be completely different.

This is one of the central functions of criminal defenses: they prevent criminal law from treating every apparently prohibited act as automatically criminal without considering its justification.

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Common Misunderstandings

“You can use any force to defend someone else.”

Not necessarily. The force generally must be reasonably necessary and proportionate to the threat.

“You must be related to the person you protect.”

Not necessarily. Most jurisdictions do not universally require a special relationship.

“The person being defended must actually have been attacked.”

Not always in the simple sense of hindsight. A reasonable mistake about the circumstances may sometimes affect the defense, depending on jurisdiction.

“Defense of others allows retaliation.”

No. The defense is intended to prevent unlawful harm, not punish someone after the danger has ended.

“You can continue using force until the attacker is seriously injured.”

No. Once the threat ends, continued force may lose its justification.

“Defense of others is identical in every state.”

No. The precise rules governing reasonable belief, mistake, proportionality, retreat, and the allocation of burdens vary among jurisdictions.

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A Practical Framework for Analyzing Defense of Others

When analyzing a defense-of-others problem, ask the following questions:

Step 1: Who was being protected?

Identify the third person whose safety was allegedly threatened.

Step 2: What was the threat?

Determine what the alleged attacker was doing.

Step 3: Was the threat unlawful?

A lawful use of force may not support the defense.

Step 4: Was the threat imminent?

Determine whether intervention was necessary at that moment.

Step 5: What did the defendant believe?

Identify the defendant’s understanding of the circumstances.

Step 6: Was that belief reasonable?

Apply the jurisdiction’s standard for evaluating mistakes and reasonable belief.

Step 7: What force was used?

Determine whether the response involved nondeadly or deadly force.

Step 8: Was the response reasonably necessary?

Consider whether the defendant had a legitimate protective purpose.

Step 9: Was the force proportionate?

Compare the seriousness of the threat with the force used.

Step 10: When did the danger end?

Determine whether the defendant continued using force after the justification disappeared.

Step 11: What does the jurisdiction require?

Finally, apply the specific statutory and case law rules governing defense of others.

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The Deeper Principle Behind Defense of Others

Defense of others reflects an important moral and legal idea: the law does not necessarily require individuals to remain passive in the face of serious unlawful violence.

At the same time, the doctrine recognizes the danger of allowing private citizens unlimited authority to use violence.

That creates a difficult balance.

On one side is the principle that people should be able to protect one another.

On the other is the principle that private individuals should not become judges, punishers, and enforcers of their own version of justice.

Defense of others therefore occupies a carefully limited space between passivity and vigilantism.

The law permits intervention under appropriate circumstances because human beings have legitimate interests in protecting one another. But it imposes boundaries because unchecked private force can itself become a source of violence.

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Key Takeaways

• Defense of others allows a person to use reasonable force to protect another person from unlawful force.
• It is generally treated as a justification defense.
• The doctrine is closely related to self-defense.
• The defendant’s reasonable belief about the threat can be critical.
• The threat generally must involve imminent or immediate danger.
• The amount of force used must generally be reasonably necessary and proportionate.
• Deadly force is subject to stricter requirements.
• Most jurisdictions do not universally require a special relationship between the defender and the person protected.
• Traditional law sometimes followed an alter ego approach, while many modern jurisdictions emphasize the defender’s reasonable perception.
• Defense of others is not a justification for retaliation or punishment after the danger has ended.
• The precise rules vary by jurisdiction.

Frequently Asked Questions

What is defense of others in criminal law?

Defense of others is a justification defense that may allow a person to use reasonable force to protect another person from an unlawful threat of force.

Is defense of others the same as self-defense?

They are closely related but protect different people. Self-defense concerns protection of oneself, while defense of others concerns protection of a third party.

Can I defend a stranger?

In many jurisdictions, yes. A special relationship is generally not required, although the precise rules vary.

Can I use deadly force to defend another person?

Potentially, but deadly force generally requires a much more serious justification, such as a reasonable belief that the other person faces an imminent threat of death or serious bodily injury.

What happens if I was mistaken about the attack?

A reasonable mistake may sometimes support a defense, depending on the jurisdiction and the precise circumstances.

Can I keep attacking someone after the threat ends?

Generally, no. Once the immediate threat has ended, continued force may become unjustified and potentially criminal.

Is defense of others an affirmative defense?

It is generally treated as a justification defense, although the procedural treatment and burden allocation vary among jurisdictions.

Does defense of others protect me from all criminal liability?

No. The defense applies only when its legal requirements are satisfied. Excessive, unnecessary, or retaliatory force may remain criminal.

Conclusion

Defense of others is an important limitation on criminal liability because it recognizes that protecting another person from unlawful violence can itself be a legally justified act.

The central question is not simply whether the defendant used force. It is whether the defendant reasonably believed that another person faced unlawful and imminent harm, whether intervention was necessary, and whether the force used was reasonable under the circumstances.

The doctrine therefore reflects the broader philosophy of criminal justification: sometimes conduct that would ordinarily be criminal becomes lawful because the circumstances make the conduct necessary to protect a more fundamental interest.

At the same time, defense of others has boundaries. The privilege to protect another person is not a privilege to punish an attacker, settle personal disputes, or continue using violence after the danger has disappeared.

Ultimately, the doctrine seeks to strike a balance between two competing principles: the right to protect human beings from serious unlawful harm and the need to prevent private violence from becoming a substitute for law itself.