Many of these breeds were originally developed as fighting dogs from cross breeding bull-baiting dogs (used to hold the faces and heads of larger animals such as bulls) and terriers. HEH HEH
My son has a rescued dog from a busted dog fighting ring. She was a bait dog. A too small part pit bull, part who knows. She is 100% fine with people but does not like and can get aggressive with bigger dogs. My Brittany male and her are very close and is not an issue. I keep her on a short leash, figuratively, under certain situations.