I have three PB mixes, two sisters from the same litter, and another that is 4 yrs younger.
The two older ones act as velociraptors upon cats, small dogs, and critters.
The smaller of the two is extremely shy and on her own will not approach people or animals.
The larger of the two has chewed through a steel wire (horse-style mesh) fence when two neighbor dogs got into a fight. It seems she likes a good party.
There is no back down in this particular dog. It is like a light switch, normally the light is off, but when it gets flipped on, IT IS ON.
Neither dog has ever shown aggression towards humans, but I will not leave my two grandchildren alone with them.
I too had always thought that aggressive Pits had to do with training, rearing, environment, but with these two I have had to realize that sometimes it is in the dog and no amount of training will take the fighter instinct out.
This is really a damn shame because I really do love dogs and I too have had a lot of success with aggressive dogs, but this time I found it is 'hard-wired' in some dogs.