Even if there has been a deliberate use of force against another person without their consent, some circumstances may excuse the action and provide a defence to a criminal charge of assault.
A person who is assaulted may defend themselves by using some force against the person attacking them. However, there are two major limitations to the use of force. First, the amount of force used in self defence must be reasonable, and no more than necessary to deal with the perceived danger. Secondly, the person who claims they were acting in self-defence cannot have done anything to provoke the attack. In other words, they cannot "set up" an assault on themselves as an excuse to strike back at another person.
Similarly, reasonable force can be used to protect other people who are under your protection. This would include close family members or others that have a close relationship with you. Reasonable force can also be used to prevent a crime. This would allow an unrelated bystander to intervene to protect an assault victim or to prevent serious property damage or loss.
A property owner can use reasonable force to protect their property. For example, a homeowner is allowed to act in order to keep someone from breaking into their home, or to remove a trespasser. Generally, personal property also can be reasonably protected by its owner. However, when protecting personal property, a person cannot hit or cause bodily harm to the individual trying to take the property. If the person trying to take the property refuses to give the item up after the owner has laid hands on it, the thief is deemed to have committed an assault.
The Criminal Code provides protection for a teacher, parent or someone who acts in the place of a parent when they use physical force to correct a child under their care. This section of the Criminal Code has been the subject of much debate over the years and has been considered by the Supreme Court of Canada. In considering the section, the court placed limits on when and how force can be used. They decided that spanking teenagers or children under the age of two, hitting a child in the head, or using objects like belts or rulers are actions that go too far. They ruled that this Criminal Code section does not justify "outbursts of violence against a child motivated by anger or animated by frustration." But the court also recognized that the section was necessary to protect a parent or caregiver as they could otherwise be charged with assault for doing something like placing an unwilling child in a chair for a five-minute time-out.
Compulsion is not a defence to an assault charge. This means that someone accused of assault cannot claim that they were forced to commit the assault by a third person.