I agree with No Bullcrap. Any unsocialized dog may fight. But you have to be extra careful to over-socialize bully breeds, because even if they play, their play might escalate unintentionally.
My 8 year old retriever rescue grew up with a Pit next door, and they played fine, because they never escalated. But one day the Pit got loose and some unsocialized Goldens tried to attack it while they were on leash. His response was instructive - The Pit stood his ground and ... the only way I can described it is that he "smiled" . It wasn't a growl or a snarl, more of a "come'on boys, let's have some fun." It was scarier than a snarl... and this was the same dog that, a few days ago, was playing on the ground with my dog on top, play biting his throat and ears.
I'm fairly confident that this Pit, which I trust completely, would have caused a lot of damage on the playground, if those Goldens had been off leash. So don't leave the Pits together unsupervised - even if they usually play... and try to continue to socialize them with many other dogs.
Suggestion: If your PitBull ever locks down on another dog (their jaws don't "lock", but they won't let go), there is a nerve on the inside of their thigh, on the line where the leg joins the belly. If you push hard with a couple of fingers, most dogs (any dog breed) will let go. It doesn't hurt the dog, but is more of a surprise.... However, in order to do this, you are putting your face in biting range, so don't do it on a strange dog, and hold the dog's head, so that when he lets go, he can't bite you instead.... Agina, only on your dog, and only if you know that he won't bite you under these circumstances... Be careful - for emergency use only....
I use this method with retrievers to get them to drop a ball... and there seem to be no bad reactions to this approach. I did suggest this to a PitBull owner in the dog park during an escalated session, and it work with no repurcussions.
