Pitbulls also have strong tendecy for aggression towards other dogs, because of the background of the breed. Not all of them have dog aggression, especially the mixed, but many do. As an instinct, it is often way too difficult to all but experts, to train them not to act on it, and many people can barely do basic training, much less realize, what sort of precautions they need to take, to prevent incidents.

This also means keeping them in places, with a lot of other dogs around - so almost every situation people live in these days - creates a big chance of them attacking other dogs. And when dogs fight, it is very common for humans to get injured, while they try to stop it, because the dogs are in a very agitated state. Since pitties are a strong breed with strong jaws, getting bit by one means usually a really bad time, even if it just an accident… which then leads to blaming the dog for their owner’s stupidity, as noted above.