An individual who is being attacked (or who is about to be attacked) has the right to defend himself with reasonable physical force. Self-defense is one of the most popular affirmative defenses that is asserted in Massachusetts courtrooms. An individual is permitted to use force to defend himself if:
Once any evidence of self-defense is presented at trial, the prosecutor bears the burden of proving beyond a reasonable doubt that the defendant was not defending himself in a lawful manner. In Massachusetts, an individual is also permitted to use deadly force to defend himself, but only if he actually and reasonably believed he was immediately in danger of death or great bodily harm. For example, an individual is permitted to use deadly force if someone is pointing a gun at him, but not if someone is threatening only to slap him.
Except in limited circumstances, a person has a duty to retreat before using force to defend himself. Retreating can take several forms including calling for assistance, holding the attacker at bay until help arrives, or simply walking away. An exception to the duty to retreat is the castle rule, which states a person who is lawfully occupying a dwelling can use force against an intruder if the resident believes the intruder is going to inflict death or great bodily injury on any person lawfully in the dwelling and the resident does not use excessive force. A dwelling is defined as any place where a person lives (even temporarily).
Self-defense is not an available argument to the person who used force in retaliation. Self-defense is permissible only when there is an emergency situation that necessitates action that is usually illegal. Therefore, once the emergency abates, the privilege to use force also goes away. Self-defense also is not a justification in the event of mutual combat. If two people make the decision to engage in a fistfight, for example, neither of them made reasonable efforts to avoid combat and neither can claim he was acting in self-defense. If, however, one of the fighters attempts to use deadly force during the brawl, the other fighter can then continue to use force to defend himself.
Typically, a person being placed under arrest cannot use force to resist the arrest (even if the arrest is unlawful). However, if the cops are using excessive force to make an arrest (which happens all the time), the person being arrested is permitted to use reasonable force to defend himself.
An individual has the legal right to use reasonable force to defend another person who is the victim (or about to be the victim) of an assault. The rule is a person can use force to defend another person if that person would be justified in using force himself in self-defense.
Finally, an individual can use reasonable force (but never deadly force) to defend his property against someone who does not have a legal right to it. This includes using force to regain possession of his property from someone who has unlawfully taken it, or removing a trespasser from his property after the trespasser has refused to leave.