It’s the breed. Sheep dogs herd sheep, Hunting dogs track prey, Pit bulls show random aggression. There is a reason many communities have a ban on owning pit bulls. Animal shelters are full of pit bulls nobody wants. They have been bred to be aggressive. Yes as previously posted, they are a ticking time bomb.
One of the things I find fascinating is that these dogs have been very carefully bred to lie. They will present as playing, wagging their tail, front legs on ground, and then go straight into an attack - with no warning. They will also do this to dogs showing submission. It is highly desired trait in dogfighting. Lot of money in dogfighting.
More info here if you want.
http://thetruthaboutpitbulls.blogspot.com/