Self-Defense in Massachusetts

Self-defense is the lawful use of force by a person who reasonably believes that force is necessary to protect against an imminent attack. In Massachusetts it is a complete defense to a charge involving the use of force. If the jury accepts it, or is left with a reasonable doubt about it, the verdict is not guilty. It applies to a shove in a bar, a punch in a kitchen, a knife drawn in a parking lot, and a fatal shooting, though the rules that govern each of those situations differ in important ways.

The jury does not consider self-defense unless the judge instructs on it, and the judge instructs on it only when the evidence at trial supports it. That evidence has to come from somewhere. It may come from the defendant’s own testimony, from cross examination of the Commonwealth’s witnesses, or from the Commonwealth’s own evidence, such as a booking photograph that shows the defendant’s injuries or a 911 recording that captures who was attacking whom. The defense builds the trial around getting that evidence into the record.

Once the evidence is in, the burden changes. The defendant does not have to prove self-defense. The Commonwealth must prove beyond a reasonable doubt that the defendant did not act in self-defense, and the judge tells the jury so. Commonwealth v. A Juvenile, 396 Mass. 108, 113 to 114 (1985). Without that instruction the jury hears only the elements of the charged offense, and a jury that believes the defendant was attacked has no legal basis to acquit on that ground. The instruction is what permits the acquittal. The same allocation applies to lack of criminal responsibility, where the Commonwealth must prove that the defendant was responsible once the issue is raised.

Massachusetts applies separate standards to nondeadly force and deadly force. Outside the home, a person must use reasonable means to avoid physical combat before using force in self-defense. The law also provides a statutory rule for an unlawful intruder in the home, limits the force a person may use to protect property, and ordinarily denies self-defense to the person who started the fight unless that person withdrew. The sections below explain each rule and the evidence a jury may consider in deciding who started the confrontation.

Attorney Joe Serpa has practiced Massachusetts criminal defense since 1995 and has tried self-defense cases involving assault, assault and battery, domestic violence, homicide, firearms, and other weapons in the District Court, the Boston Municipal Court, and the Superior Court.

The Right to the Instruction

The standard for obtaining the instruction is favorable to the defendant. When deciding whether to instruct the jury on self-defense, the judge views the evidence in the light most favorable to the defendant. If any reasonable view of that evidence supports the claim, the jury must decide it under the correct standard. A judge who refuses the instruction on a record that supports it commits an error that can require a new trial.

A defendant who does not testify may still be entitled to the instruction. If the Commonwealth’s own witnesses describe an encounter that could have been defensive, or if cross examination draws that account out of them, the evidence is in the record whether or not the defendant takes the stand. Counsel decides early which route the evidence will take, and that decision shapes the entire trial.

Massachusetts common law governs self-defense. There is no single self-defense statute. The judge instructs the jury from the Massachusetts model instructions, and the District Court instructions on self-defense, Instructions 9.260 through 9.263, were most recently revised in October 2024 and February 2026.

Nondeadly Force

A defendant who used nondeadly force is entitled to a self-defense instruction when any reasonable view of the evidence supports a reasonable doubt on three questions.

1. Did the defendant have a reasonable concern for personal safety?
2. Did the defendant use all proper and reasonable means to avoid physical combat?
3. Was the force reasonable and proportionate in the circumstances?

The Supreme Judicial Court describes the third requirement by stating that “the degree of force used was reasonable in the circumstances, with proportionality being the touchstone for assessing reasonableness.” Commonwealth v. King, 460 Mass. 80, 83 (2011). See also Commonwealth v. Franchino, 61 Mass. App. Ct. 367, 368 to 369 (2004).

The concern for safety must arise from an overt act by the other person. An overt act may consist of words, a gesture, or another action that could create an actual and objectively reasonable concern for immediate personal safety. The threat does not have to be a threat of death or serious injury. A reasonable fear of being struck is enough to justify a proportionate response.

Deadly Force

Deadly force means force intended or likely to cause death or great bodily harm. A knife, a firearm, a bottle swung at the head, or a sustained beating may each qualify. A defendant may use deadly force only when the defendant held an actual and reasonable belief that death or serious bodily injury was imminent and that deadly force was necessary to prevent it. Commonwealth v. Grassie, 476 Mass. 202, 210 (2017); Commonwealth v. Pike, 428 Mass. 393, 396 (1998).

The Supreme Judicial Court has called the deadly-force and nondeadly-force rules “distinct, self-contained definitions of self-defense” and “mutually exclusive.” The evidence concerning the force the defendant used determines which standard applies. Commonwealth v. Walker, 443 Mass. 213, 217 (2005).

Nondeadly force, such as a push, shove, or punch, requires a genuine and reasonable concern for personal safety. It does not require an imminent threat of death or serious bodily injury. Commonwealth v. Baseler, 419 Mass. 500, 502 to 503 (1995).

The distinction changes the Commonwealth’s burden at trial. When the evidence supports a nondeadly-force instruction but the judge gives only the deadly-force instruction, the jury applies a standard that requires a greater danger before the defendant may act. That error can require reversal. Commonwealth v. Baseler, 419 Mass. 500, 502 to 504 (1995).

The charged offense does not decide which instruction applies. The judge must examine the force described by the evidence. A single punch in response to being grabbed may support the nondeadly-force instruction even when the complaint alleges a serious assault. Where the evidence leaves the level of force in genuine dispute, the judge must give both instructions.

The Duty to Retreat

Outside the home, a person must use all proper and reasonable means to avoid physical combat before using force. A safe means of escape that was reasonably available can defeat a self-defense claim. Massachusetts follows a retreat rule rather than a stand-your-ground rule. Commonwealth v. Pike, 428 Mass. 393, 399 (1998); Commonwealth v. Mercado, 456 Mass. 198, 209 (2010).

The duty does not require a person to place themselves in additional danger, exhaust every conceivable means of escape, or use every possible means of flight. Commonwealth v. Benoit, 452 Mass. 212, 226 to 227 (2008). The question is whether the circumstances offered a safe and reasonable way to avoid the confrontation.

In Commonwealth v. Leoner-Aguirre, 94 Mass. App. Ct. 581 (2018), the Appeals Court rejected a self-defense claim where the defendant shot the victim in the back as the victim fled on a public street and the evidence showed a clear opportunity to retreat.

The jury considers all the circumstances, including the distance between the participants, their relative size and number, the presence of weapons, the location, the available exits, and whether summoning help or leaving would have ended the danger. The defense should document the scene, measurements, exits, obstacles, and timing before those conditions change.

The Castle Law

M.G.L. c. 278, § 8A removes the duty to retreat in a defined home-intrusion setting. An occupant charged with killing or injuring a person who was unlawfully in the dwelling may rely on the statute when four conditions are met.

1. The defendant occupied the dwelling.
2. The other person was unlawfully in the dwelling.
3. The defendant reasonably believed that the intruder was about to inflict death or great bodily injury on the defendant or on another person lawfully present.
4. The defendant used reasonable means to defend against that threat.

When the evidence establishes each requirement, the occupant has no duty to retreat from the unlawful intruder. The statute does not eliminate the separate requirements of reasonable belief and proportionate force.

A Person Lawfully in the Home

The castle law does not apply when the other person remains lawfully in the home as a guest, family member, or cohabitant, even if that person begins a life-threatening attack. Commonwealth v. Peloquin, 437 Mass. 204, 208 (2002). The ordinary retreat rule continues to apply, which is why the statute so rarely helps in a domestic violence prosecution.

A person who entered lawfully may become a trespasser by remaining after a lawful demand to leave under M.G.L. c. 266, § 120. The evidence must establish when the right to remain ended and where the confrontation occurred.

Multi-Unit Housing

For castle-law purposes, a dwelling means the space the occupant possesses and exclusively controls. Massachusetts courts have held that common hallways, shared stairwells, porches, and driveways in multi-unit housing fall outside the statute. The exact location of the confrontation can therefore determine whether the ordinary duty to retreat applies.

Reasonable and Proportionate Force

The castle law does not authorize deadly force in response to every unlawful entry. The defendant must still have a reasonable belief that death or great bodily injury is imminent, and the force must remain proportionate to the threat.

The Civil Counterpart

A separate statute, M.G.L. c. 231, § 85U, applies the same rule in civil law. A lawful occupant who was in the dwelling, who reasonably believed an unlawful occupant was about to inflict death or great bodily injury, and who used reasonable means of defense is not liable in damages for the intruder’s death or injuries, and has no duty to retreat. Outside that setting, Massachusetts provides no general civil immunity for acts of self-defense, and an acquittal in the criminal case does not by itself bar a civil suit.

The First Aggressor

The right of self-defense ordinarily cannot be claimed by a person who provoked or initiated the assault. The rule has one important qualification. A first aggressor regains the right to defend if that person withdraws in good faith from the conflict and announces the intention to retire. Commonwealth v. Maguire, 375 Mass. 768, 772 (1978). Whether a withdrawal occurred, and whether it was communicated, is a question for the jury.

The first aggressor is not necessarily the person who threw the first punch. A person may become the first aggressor by escalating a nondeadly confrontation through the threat or use of deadly force. Commonwealth v. Chambers, 465 Mass. 520, 528 to 530 (2013); Commonwealth v. Souza, 492 Mass. 615 (2023). A person who is shoved and answers with a knife has introduced deadly force into an encounter that did not contain it.

Nonthreatening words alone do not make a defendant the first aggressor. Speaking first, speaking loudly, or arguing does not by itself eliminate the right to use lawful defensive force, and the Supreme Judicial Court has directed judges to say so when a first-aggressor instruction is given. Commonwealth v. Harris, 464 Mass. 425, 433 to 436 (2013).

Excessive Force and Voluntary Manslaughter

A defendant who had the right to use some force but used more than was reasonably necessary loses the complete defense. In a homicide case, that finding does not end the analysis. The Supreme Judicial Court has held that when a defendant was privileged to use force in self-defense but the Commonwealth proves that the force was excessive, the crime is voluntary manslaughter rather than murder. Commonwealth v. Boucher, 403 Mass. 659 (1989); Commonwealth v. Walker, 443 Mass. 213 (2005).

The Model Jury Instructions on Homicide treat excessive force in self-defense as a mitigating circumstance that the Commonwealth must negate beyond a reasonable doubt to obtain a murder conviction. A judge who instructs on self-defense in a homicide case without explaining that consequence commits reversible error.

The same point applies outside homicide. In an assault prosecution, a jury that finds the defendant used excessive force may still consider the defensive context on the question of intent, and counsel may argue it at sentencing. The finding of excess does not convert a defensive act into an unprovoked one.

Defense of Another

A person may use reasonable force to defend another person. The defender may use the degree of force that the person being protected could lawfully have used, judged by what the defender reasonably believed was necessary.

The substantive distinctions between deadly and nondeadly force, proportionality, retreat, and the Commonwealth’s burden all apply. Defense of another requires its own jury instruction, and counsel must request and preserve that instruction when the evidence supports it.

The evidentiary rules differ from self-defense. In Commonwealth v. Rateree, 495 Mass. 610 (2025), the Supreme Judicial Court declined to extend the Adjutant rule to a claim based only on defense of another. The court identified the risk that propensity evidence concerning the alleged victim, the defendant, and the person defended could confuse the issues, cause unfair prejudice, and divert the trial.

Prior violent acts by the alleged victim therefore require a separate admissibility analysis when the defendant relies on defense of another. When the evidence independently supports self-defense, counsel should request that instruction and address the first-aggressor evidence under the rules that apply to that distinct claim.

Defense of Property

The law permits far less force to protect property than to protect a person. A person may use reasonable nondeadly force to eject a trespasser or to defend or regain momentarily interrupted possession of personal property. The force must be appropriate in kind and suitable in degree to accomplish that purpose. Commonwealth v. Haddock, 46 Mass. App. Ct. 246, 249 to 250 (1999).

Deadly force is never justified to protect property alone. The Supreme Judicial Court stated the limit more than a century ago: a person may defend possession “by the use of reasonable force, short of wounding or the employment of a dangerous weapon.” Commonwealth v. Donahue, 148 Mass. 529, 531 (1889), quoted in Haddock. A person who strikes a thief with a weapon to recover a phone has exceeded what the law allows for property, and the case then depends on whether the thief’s own conduct created a threat to the person.

Once the evidence raises defense of property, the Commonwealth must prove beyond a reasonable doubt that the force was excessive in kind or degree. The doctrine most often arises in shoplifting confrontations, disputes over repossession, and arguments over who may remain on a property.

Force Against a Police Officer

Massachusetts does not recognize a right to resist arrest. In Commonwealth v. Moreira, 388 Mass. 596, 601 to 602 (1983), the Supreme Judicial Court held that a person may not use force to resist an arrest by someone the person knows or has good reason to believe is a police officer performing official duties, regardless of whether the arrest was lawful. The resisting arrest statute, M.G.L. c. 268, § 32B, states the same rule: the unlawfulness of the arrest is not a defense.

The one exception is excessive force. Where an officer uses excessive or unnecessary force to subdue a person, the person may defend by using the force that reasonably appears necessary, whether or not the arrest itself was lawful. The right ends as soon as the person knows, or reasonably should know, that the officer will stop using force if the person stops resisting. Whether the officer’s force was excessive and whether the response was reasonable are questions for the jury.

These cases are common in the Boston Municipal Court and the District Court, often charged as disorderly conduct and resisting arrest together with assault and battery on a police officer. Body-worn camera footage, booking video, and the timing of any injuries frequently decide them.

Mutual Combat and Consent

Agreeing to fight is not a defense. Massachusetts has held since Commonwealth v. Collberg, 119 Mass. 350 (1876), that when two people agree to fight and do so, each has committed an assault, and it is immaterial who struck first. A person cannot consent to being beaten.

Self-defense survives that rule. A person who agreed to a fistfight and then faced a knife, or who tried to stop and was pursued, may still have acted defensively at the moment force was used. The question becomes who escalated, who withdrew, and whether the force used at that point was proportionate. The firm’s article on self-defense and mutual combat in Massachusetts domestic violence cases explains how these principles apply when both parties used force.

Self-Defense in Domestic Violence Cases

Self-defense often arises in Massachusetts domestic violence cases. The person who called the police may have started the physical confrontation, and an arrest does not decide who acted first.

The defendant may be able to present evidence of earlier threats, violence, or abuse to explain why the defendant reasonably perceived immediate danger. The purpose and admissibility of that evidence depend on what the defendant knew and whether the evidence addresses the defendant’s state of mind or the separate question of who started the confrontation.

Violence or Threats Known to the Defendant

To prove the reasonableness of the defendant’s apprehension, the defense may offer evidence of the complainant’s prior acts of violence, prior threats against the defendant, and reputation for violence when the defendant knew of that history at the time of the incident. Commonwealth v. Pidge, 400 Mass. 350, 353 (1987); Commonwealth v. Edmonds, 365 Mass. 496, 499 to 501 (1974); Mass. G. Evid. § 404(a)(2)(C).

The jury may consider that history when deciding whether the defendant’s concern for immediate personal safety was reasonable. Conduct that appears ambiguous when viewed in isolation may mean something different to a person who knows about earlier threats or violence.

Evidence of Abuse Under M.G.L. c. 233, § 23F

M.G.L. c. 233, § 23F permits a defendant who claims self-defense or defense of another to offer evidence that the defendant is or has been a victim of abuse. The statute also permits qualified expert testimony concerning common effects of abuse.

That evidence may help the jury evaluate why the defendant perceived an imminent threat and whether that perception was reasonable. Counsel must identify the issue early, determine whether expert testimony is appropriate, and satisfy the applicable disclosure and evidentiary requirements.

Prior Violence and the Identity of the First Aggressor

The Adjutant rule concerns specific acts of violence by the alleged victim when the identity of the first aggressor is genuinely disputed. It can apply even when the defendant did not know about those acts at the time of the charged incident.

In Commonwealth v. Adjutant, 443 Mass. 649 (2005), the Supreme Judicial Court held that a trial judge has discretion to admit evidence of the alleged victim’s specific prior acts of violence when the defendant raises self-defense and the identity of the first aggressor remains genuinely disputed. The jury may consider the incidents when deciding who probably initiated the violence. Commonwealth v. Adjutant, 443 Mass. 649, 664 to 665 (2005).

This evidence serves a different purpose from evidence of threats or violence known to the defendant. Known acts may explain the defendant’s state of mind. Adjutant evidence addresses the factual identity of the first aggressor regardless of the defendant’s prior knowledge.

The Scope and Timing of the Prior Act

When the alleged victim initiated a violent incident, the judge may admit the entire event rather than an isolated portion that obscures who started it. Commonwealth v. Deconinck, 480 Mass. 254, 263 (2018); Commonwealth v. Souza, 492 Mass. 615, 617 (2023).

An act offered under Adjutant may have occurred before or after the charged offense. Commonwealth v. Andrade, 496 Mass. 144, 147 to 148 (2025); Commonwealth v. Chambers, 465 Mass. 520 (2013).

The trial judge decides admissibility. The proposed incident must relate to a genuinely disputed first-aggressor question, satisfy the other evidence rules, and have probative value that outweighs the risk of unfair prejudice. Commonwealth v. Souza, 492 Mass. 615, 626 (2023); Commonwealth v. Rateree, 495 Mass. 610, 621 (2025).

The Defendant’s Own Record

Offering the alleged victim’s violent history is a decision with a cost. Once the defense opens that door, the Commonwealth may seek to introduce specific incidents of the defendant’s own prior violence. In a case decided in August 2026, the Supreme Judicial Court held that trial counsel’s decision not to offer Adjutant evidence was not ineffective where the defendant, and not the victim, was the one with an assault and battery conviction. The firm’s August 2026 decisions roundup covers that decision.

Rule 14.3 Notice and Prosecution Rebuttal

Massachusetts Rule of Criminal Procedure 14.3(c) requires the defense to give written notice of proposed first-aggressor evidence no later than twenty-one days after the pretrial hearing unless the judge sets another time for good cause. The Commonwealth ordinarily has thirty days after receiving the defense notice to disclose proposed rebuttal evidence.

The defense notice must briefly describe each incident, provide its date and location to the extent practicable, and identify the witnesses the defense may call. A motion in limine may help define an admissibility dispute, but it does not replace the written notice. A party that fails to comply with the rule risks exclusion of its evidence concerning the identity of the first aggressor.

The Commonwealth may respond with evidence of the alleged victim’s community reputation for peacefulness. Under Commonwealth v. Morales, 464 Mass. 302, 310 to 312 (2013), the Commonwealth may also seek to introduce specific incidents of the defendant’s prior violent conduct. The rule concerns particular incidents, not the defendant’s entire criminal record.

The judge may admit proposed Morales evidence only when it satisfies the other evidence rules and its probative value outweighs the risk of unfair prejudice. The rule requires reciprocal notice. When the judge admits specific-act evidence from either side, the judge must give the jury an appropriate limiting instruction at admission and again during the final charge.

The article on Adjutant evidence and prosecution rebuttal provides a more detailed treatment of the governing decisions, the distinct uses of prior-incident evidence, and the Rule 14.3 procedure.

Investigating First-Aggressor Evidence

Counsel should investigate possible first-aggressor evidence early. Police reports, court records, recordings, photographs, medical records, and witnesses may identify admissible evidence concerning another incident. A criminal charge or docket label does not establish who initiated the violence.

The proponent must still satisfy the ordinary evidence rules. A witness with personal knowledge may be necessary to prove what occurred. Hearsay and authentication objections may limit a police report, screenshot, recording, or copied message. Testimonial statements offered by the Commonwealth may also raise a separate Confrontation Clause question. The guide to digital evidence in Massachusetts criminal cases explains authentication and objection rules for messages, recordings, and other electronic evidence.

Charges That May Involve Self-Defense

Self-defense and defense of another may apply to any criminal charge involving force when the evidence supports the required elements. The court selects the deadly-force or nondeadly-force instruction from the force shown by the evidence rather than from the charge label alone.

• Assault and battery on a family or household member, M.G.L. c. 265, § 13M. Prior abuse, the defendant’s knowledge, and the identity of the first aggressor may all affect the defense.
• Simple assault and battery, M.G.L. c. 265, § 13A. A push, shove, punch, or other nondeadly force may require the reasonable-concern and proportionality instruction.
• Assault and battery by means of a dangerous weapon, M.G.L. c. 265, § 15A. The court must determine from the evidence whether the defendant used deadly or nondeadly force.
• Strangulation or suffocation, M.G.L. c. 265, § 15D. The identity of the first aggressor and the amount of force used may remain disputed in a household prosecution.
• Assault and battery on a police officer and resisting arrest. The Moreira rule governs, and the defense depends on whether the officer’s force was excessive.
• Firearms and weapons charges. Lawful defensive use may address the conduct alleged in an assault count. A separate possession, licensing, or carrying charge depends on its own elements. A licensing authority may also suspend or revoke a license to carry on a determination of unsuitability under M.G.L. c. 140, § 121F, which rests on behavior rather than on a conviction and can therefore survive a favorable result in the criminal case.
• Homicide charges. The evidence may require instructions on self-defense, defense of another, or both, together with the deadly-force and retreat rules and the excessive-force mitigation described above.

Self-Defense Before Trial

Self-defense is decided by a jury, but the facts that support it matter from the first day of the case.

Many assault and battery cases begin with an application for a criminal complaint rather than an arrest. At the clerk-magistrate hearing, the accused person may present the defensive context, the complainant’s role in starting the encounter, and any injuries the accused sustained. The clerk-magistrate decides whether probable cause exists and, where discretion is available, whether a complaint should issue at all. A defensive account presented with supporting evidence at that stage can end the matter before it becomes a criminal case.

When the Commonwealth seeks pretrial detention under M.G.L. c. 276, § 58A, the evidence of who started the encounter bears directly on whether the accused is dangerous. A dangerousness hearing is the first occasion on which a judge weighs the defensive account against the complainant’s, and the record made there can shape the case that follows.

Early Investigation and Trial Preparation

The defense should preserve scene evidence before conditions change. Photographs, measurements, surveillance video, witness accounts, emergency calls, medical records, and photographs of the defendant’s injuries may establish the threat, the available exits, the sequence of force, and the identity of the first aggressor.

Prior-incident evidence also requires time. Counsel may need court records, police reports, recordings, photographs, medical records, or witnesses before serving a Rule 14.3 notice. The notice deadlines make early investigation part of preserving the defense rather than a task that can wait until trial.

The defendant’s statements can affect whether the evidence supports self-defense. A person questioned after a violent encounter should understand the right to remain silent in Massachusetts before giving police a recorded account, consenting to a device search, or discussing the incident on a recorded station telephone. An account given in the first hour, before the person has slept or spoken to counsel, is the account the Commonwealth will use.

Attorney Serpa begins a self-defense case by identifying the governing force standard, documenting the scene and injuries, locating witnesses, reviewing prior incidents, and preserving the request for the correct jury instruction. His Massachusetts criminal defense results include acquittals in cases involving allegations of serious violence. The firm’s page on trial and motion practice describes how those requests are made and preserved.

To discuss a Massachusetts self-defense or defense-of-another case, contact Serpa Law Office for a free consultation. The Boston office is at 20 Park Plaza, Suite 400A. The Quincy office is at 500 Victory Road, Suite 400A.

Serpa Law Office can be reached at 617.936.0201.