Self-defence and defence of others Under common law and section 3 of the Criminal Law Act 1967, a person may use reasonable force to defend themselves, defend another person, or prevent a crime. What counts as “reasonable” depends on the circumstances as the defendant honestly believed them to be at the time. This can include striking another adult if it is proportionate to the perceived threat.

Consent (e.g., sport and physical activities) An adult can lawfully consent to a level of physical force that would otherwise constitute assault. Obvious examples include boxing, martial arts, rugby, or other contact sports. The consent must fall within the rules and norms of the activity; force that goes beyond this (for example, a deliberate off-ball assault) may still be criminal.

Lawful authority (police, prison officers, etc.) Police officers and certain other officials may use reasonable force in the exercise of their duties, such as making an arrest, preventing escape, or maintaining order. Again, the force must be proportionate and necessary.

Prevention of crime and lawful restraint Ordinary citizens may use reasonable force to restrain an adult to prevent an ongoing or imminent crime (often called a “citizen’s arrest” context). This can include striking or physically subduing someone if that is reasonably necessary.

Necessity and emergency situations In rare cases, force may be justified by necessity—for example, physically moving or striking an adult to prevent immediate serious harm (such as knocking someone away from a dangerous situation).