Self-defence means fighting off something or another person to protect yourself and maybe others. Ways of self-defence include martial arts or using a weapon. Sometimes, self-defense can cause serious harm to the other person. In most nations, you cannot be prosecuted for this harm. In the United States, an act of self-defence can only count as self-defence if the victim is in a situation that can cause them serious injury or death. In international law all persons have the right to self-defence.