Self-defense (self-defence in some varieties of English) is a countermeasure that involves defending the health and well-being of oneself from harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many jurisdictions.
Physical self-defense is the use of physical force to counter an immediate threat of violence. Such force can be either armed or unarmed. In either case, the chances of success depend on various parameters, related to the severity of the threat on one hand, but also on the mental and physical preparedness of the defender.