Wrestling is the act of physical engagement between two unarme persons, in which each wrestler strives to get an advantage over or control of their opponent. Physical techniques which embody the style of wrestling are clinching, holding, locking, and leverage. Avoiding techniques likely to lead to serious injury, ritual fighting, but its basic principles are closely related to those of military hand-to-hand combat or self-defence systems. Many styles of wrestling are known all over the world and have long histories, and sport wrestling (particularly amateur wrestling) has been an Olympic sport for over one hundred years.