pit bull terrier,fighting dog developed in 19th-century England out of the from bulldog and a terrier . See Staffordshire terrier.ancestry. The name is applied to several breeds of dogs, including the bull terrier, American Staffordshire terrier (also called the American pit bull terrier) and Staffordshire bull terrier. Although these dogs were originally bred and trained to display aggression against other dogs, aggression against humans was not encouraged because, even while fighting, the dogs had to be handled by their trainers. Dogs displaying this trait were not selected for breeding. However, the resurgence of dogfighting—illegal in the United States, Great Britain, and many other countries—has led to irresponsible breeders encouraging such traits in their animals and mistreating them in order to induce a vicious temperament. Well-publicized attacks on people by dogs identified as pit bulls have led to the passing of legislation in some jurisdictions banning or restricting the keeping of the breeds. Some humane societies routinely euthanize pit bulls that come into their possession, deeming them unsuitable for adoption.