Section 1983 is a federal statute that authorizes a civil action against a person who, acting under color of state law, deprives someone of rights secured by the Constitution or federal law. It is an important remedy, but the statute does not itself identify every right or resolve every question about who may be sued.
Start with the specific right and conduct
A useful first step is to identify the governmental action, the person or entity involved, and the constitutional or federal right allegedly affected. The details matter: a claim centered on a search, use of force, due process, speech, or conditions of confinement can involve different legal standards.
Individual and municipal defendants are not interchangeable
Section 1983 speaks to a person acting under color of state law. Claims against a municipality involve additional rules. The Supreme Court’s decision in Monell holds that a local government is not liable solely because it employs a person who allegedly violated the Constitution; the challenged conduct must be connected to the municipality’s policy or custom.
Massachusetts also has a state civil-rights statute
Massachusetts General Laws chapter 12, sections 11H and 11I create a separate statutory framework for interference with rights by threats, intimidation, or coercion. Whether that statute, Section 1983, or another remedy fits a situation depends on the evidence and the applicable deadline.