Does Self-Defense Apply When You Defend Someone Else?

The legal right to use self-defense extends to defending others. However, like self-defense, defense of others is subject to important conditions and limitations.

What Are the Laws on Defending Others?

Every state permits lawful self-defense. If someone faces an imminent threat of harm, they can use reasonable force to protect themselves. Similarly, the law allows a person to intervene and use reasonable force to protect someone else from imminent harm. In this defense-of-others context, the intervenor "steps into the shoes" of the victim (or third party).

Limits on Force When Protecting Another Person

The same limits on the use of force that apply to self-defense generally apply to the defense of others.

Necessity, Proportionality, and Reasonable Belief

Three key components of self-defense and defense of others are: (1) necessity, (2) proportionality, and (3) reasonable belief. So, for either defense to succeed, the person must:

• reasonably believe that force is necessary to protect oneself or another from an aggressor's imminent and unlawful force, and
• use only as much force as a reasonable person would believe necessary to stop the threatened harm.

When an intervenor enters the fray to defend a third party, they are essentially using the third party's right to self-defense.

Examples of Self-Defense and Defense of Others

Suppose Alex attacks Victor. Under many circumstances, Victor would have the right to defend himself with force. If charged with a crime, Victor would claim self-defense.

Now, suppose Alex attacks Victor, and Ivan jumps to Victor's defense. If Ivan forcefully repels Alex to protect Victor, and the prosecution later charges Ivan with assault, he could claim defense of others.

Is Deadly Force Permissible When Defending Others?

Yes. But the use of deadly force is only justified if the intervenor reasonably and honestly believed that the aggressor intended to kill, rape, kidnap, or cause serious bodily harm to the third party. The same standard applies to the use of deadly force in self-defense.

Example of State Law on Defense of Others

Here's an excerpt from Colorado's law on self-defense and defense of others:

(1)... [A] person is justified in using physical force upon another person in order to defend himself or a third person from what he reasonably believes to be the use or imminent use of unlawful physical force by that other person, and he may use a degree of force which he reasonably believes to be necessary for that purpose.

(2) Deadly physical force may be used only if a person reasonably believes a lesser degree of force is inadequate and:

(a) The actor has reasonable ground to believe, and does believe, that he or another person is in imminent danger of being killed or of receiving great bodily injury; or ...

(c) the other person is committing or reasonably appears about to commit [kidnapping, robbery, sexual assault, first-degree assault, or second-degree assault].

(Colo. Rev. Stat. § 18-1-704 (2025).)

Mistaken Belief of Harm: Does Defense of Others Still Apply?

Historically, many states took the position that the intervenor was the victim's "alter ego." The alter-ego approach was problematic because it strictly limited the intervenor to the rights possessed by the victim being defended. If the intervenor was mistaken (even reasonably), they couldn't claim defense of others.

For instance, say a plain-clothed police officer is wrestling with a suspect, but the intervenor reasonably believed the suspect was being attacked. Under the alter-ego doctrine, the suspect didn't have a right to use self-defense against the officer, so the intervenor wouldn't either.

Now most jurisdictions allow defense of others as long as the intervenor's belief was reasonable—even if ultimately mistaken.

Proving Defense of Others in a Criminal Case

A person claiming self-defense or defense of others in a criminal case must typically present evidence in support of their defense—that is, some proof that the other person "started it" and that they acted reasonably to repel the attack. The prosecution must then disprove the self-defense claim beyond a reasonable doubt. It's usually up to a jury to decide if the prosecution disproves the defense.

Other Legal Rules Affecting a Defense-of-Others Claim

Self-defense and defense-of-other rules have more nuances than those discussed above. Other legal requirements that might apply include:

• duty to retreat
• stand your ground laws
• castle doctrine
• aggressor status changes
• aggressor withdraws, and
• provocation rules.

State laws can (and do) vary on these rules.

Working With a Lawyer

Any defense will depend on the laws in that jurisdiction and the facts of the case. It's important to get legal guidance when considering raising a defense-of-others claim.