The only defense for a dog is there bitting. Dogs will bite people if they feel threatened or feel like they or their owners are in harm.
Biting, snapping, lunging, barking, and snarling for dogs are there main defenses, and if a dog does this even when people are just walking buy you dog is considered an aggressive dog (Kennith Morgan Phillips). So if a dog bites you have to think that was the person that the dog bit was doing any thing that they were doing something that made the dog go after them and bit them or was the dog in an aggressive mood and bit that person for no reason. But yes there are some dogs out there that are mean and shouldn't be out and in sight of other people. And when them dogs do get out they do after people and bite them because they don't know them. But at that time it should be the owners fault because they couldn't keep the dog locked up, or even the owner could be abusing the dog and that asked them be naturally aggressive. But that is the owners fault and not the dog’s