Self-defense is a complete defense in Massachusetts. If you used force because you were attacked or about to be attacked, and you stayed within the limits the law sets, you are not guilty. You do not have to prove you acted in self-defense. Once the issue is in the case, the Commonwealth must prove beyond a reasonable doubt that you did not. The rules come from the District Court model jury instructions on self-defense, Instructions 9.260 through 9.263.
At a Glance: Self-Defense
No burden on you
the Commonwealth must disprove self-defense beyond a reasonable doubt
Two levels of force
deadly force requires a reasonable belief of immediate danger of death or serious harm
Avoid combat first
use reasonable, safe ways out; no retreat required from an unlawful intruder at home
If it succeeds
not guilty
The source: District Court Model Jury Instructions 9.260–9.263; G.L. c. 278, § 8A (castle law)
The Commonwealth’s Burden
When the evidence raises self-defense, the Commonwealth must prove the elements of the crime and also prove beyond a reasonable doubt that you did not act in lawful self-defense. There is no burden on you to prove you were justified. If the Commonwealth falls short, the jury must find you not guilty.
The instructions give the Commonwealth five ways to disprove self-defense. It needs to prove only one:
No actual fear. You did not actually have the required concern for your safety.
No reasonable fear. A reasonable person in your circumstances would not have had that concern.
You did not try to avoid the fight. You did not take all reasonable steps to avoid physical combat before using force.
Too much force. You used more force than was reasonably necessary.
You started it and did not withdraw. Used only when there is evidence you were the first aggressor (explained below).
Non-Deadly vs. Deadly Force
The level of force you used decides which version of the rules applies. The judge decides whether the force was non-deadly or deadly as a matter of law, or, if the evidence could support either, leaves that question to the jury.
Non-deadly force (Instruction 9.261). You must have had an actual and reasonable concern for your immediate personal safety.
Deadly force (Instruction 9.262). The standard is higher. You must have actually and reasonably believed you were in immediate danger of death or serious bodily harm from which you could save yourself only by using deadly force.
Either way, there must be an overt act—words, a gesture, or some other action—that could create that fear. A person cannot lawfully act in self-defense unless they are attacked or immediately about to be attacked. A reasonable mistake is allowed: a person who reasonably, but wrongly, believed they were in danger may still use force to defend themselves.
The Right Ends When the Danger Ends
The law does not permit retaliation or revenge. Self-defense arises from necessity and ends when the necessity ends. Force used to chase down an attacker, to strike back out of anger after the attacker has been neutralized or disarmed, or to head off some future attack is not self-defense.
Duty to Avoid Combat and Retreat
Before using force, a person must use the reasonable means available to avoid the fight. Under Instruction 9.261, the Commonwealth can defeat self-defense by proving you used force without using avenues of escape that were reasonably available and would not have exposed you to further danger. The jury may consider where the incident happened and whether you could have walked away, gotten to safety, called for help in time, or held the attacker at bay. It may also consider that a person under threat may have to decide quickly and under emotional strain.
For deadly force, the instruction is clear that this is not an absolute duty. You must retreat unless you reasonably believe you cannot safely do so. You need not put yourself in danger or use every means of escape short of death before defending yourself.
The Castle Law: No Duty to Retreat at Home
G.L. c. 278, § 8A removes the duty to retreat in one setting. A lawful resident of a dwelling, such as a house or apartment, is not required to retreat before using reasonable force against an unlawful intruder, if the resident reasonably believes the intruder is about to kill or seriously injure them or another person lawfully in the dwelling, and reasonably believes force is necessary to protect themselves or that person.
The castle law has limits. It does not apply to a confrontation with someone who is lawfully in the home, such as a guest or family member, and the instruction notes it does not reach encounters outside the dwelling, such as a driveway, porch, or outside stairs.
How Much Force Is Too Much
The force used must be reasonably necessary. That is judged “with due regard for human impulses and passions,” not with hindsight. The jury may consider the relative physical abilities of the people involved, how many were on each side, whether weapons were used and by whom, the room to maneuver, how the force was used, the scope of the threat, and whether you had to decide quickly.
The First Aggressor
Generally, a person who was the first to use or threaten force has no right to self-defense unless they withdrew from the conflict in good faith and clearly communicated, by words or conduct, that they were ending it. In the deadly-force instruction, if you started a fight with non-deadly force but the other person escalated to deadly force, such as turning a fistfight into a knife fight, you may claim self-defense when responding to that escalation.
Evidence About the Other Person
The instructions allow the jury to hear certain evidence about the alleged victim. Threats or acts of violence by the alleged victim, and a reputation for violence or quarreling, may be considered on your state of mind if you knew about them. On the separate question of who attacked whom first, the jury may consider the alleged victim’s threats against you and specific past acts of violence even if you did not know about them.
Why a Lawyer Matters
Self-defense cases are won on the facts: who moved first, what was said, how much room there was, and what the witnesses and videos really show. Because the burden is on the Commonwealth, the defense’s job is to put that evidence in front of the jury clearly. I have defended criminal cases for 23 years. If you were charged after defending yourself, contact my office or call 781-393-5900.
Defense of property: the narrower rules for using force to protect property.
Duress: a defense for crimes committed under an immediate threat from another person.
Entrapment: a defense where law enforcement induced the crime.
Resisting arrest (G.L. c. 268, § 32B): a separate charge often filed after a confrontation with police.
Disclaimer
This information is for general educational purposes only and not legal advice. Laws change. For advice about a specific case, speak with a licensed Massachusetts attorney.
