Parkour is a physical activity that is difficult to categorize. It is often mis-categorized as a sport or an extreme sport; however, parkour has no set of rules, team work, formal hierarchy, or competitiveness. It is an art or discipline that resembles self-defense in the ancient martial arts. According to David Belle, "the physical aspect of parkour is getting over all the obstacles in your path as you would in an emergency. You want to move in such a way, with any movement, as to help you gain the most ground on someone or something, whether escaping from it or chasing toward it." Thus, when faced with a hostile confrontation with a person, one will be able to speak, fight, or flee. As martial arts are a form of training for the fight, parkour is a form of training for the flight. Because of its unique nature, it is often said that parkour is in its own category.