Many people automatically start to beat on the dog to break them up. Others turn the hose on them , but none of those methods work with the Pitbull. The best ,  and most humane way to stop a fight if two dogs get hold of eachother is to use a Breakingstick / Partingstick.

Known by both names. It is a very hard piece of wood or some other material suitable for the purpose of spreading a dog's jaws apart. It is usually about 5 to 8 inches in length , wedge shaped and contoured to prevent injury to the dog's lips. Its width is about 1 to 2 inches.

Two people are needed to part the dogs.

Each person takes his dog by the scruff of the neck

( not the collar, for that will choke the dog).

The dogs , being Pitbulls , will not want you to separate them , and will hold on to each other. Insert the breaking stick behind the eye teeth and begin working it into the mouth with a rockingchair prying motion.

One of the  dogs will probably come loose before the other, and it is important to keep the breaking stick in his mouth to keep him from grabbing the other dog again. With Pitbullīs  you don't have to worry about one of them biting you , at least not on purpose ! 

But if your dog has hold of some other breed, make sure that the other guy keeps that breaking stick in the other dogīs mouth , or he is likely to bite both of you !

So, always bring a breaking stick with you while walking your dog. Its an easy tool to separate dogs if they come in to a fight...

Now, I have a few comments about the mechanics of a dog fight. The first is that ALL dogs use their hind quarters for both leverage and mobility and it is the most important place to start when stopping a fight. Once you remove the back end from the equation you've stopped 75% of a fight. It's amazing, most of the time you'll see the dogs quit shaking and moving as soon as they feel their hind quarters locked by your legs. They almost freeze! Once their movement is under control it's super easy to grab the neck and insert the stick.

Holding the neck with your free hand helps prevent a dog from biting you while stopping the fight. I've broken lots of accidental fights and all those times I have never been bitten by an APBT. But, I have been biten by other breeds because of the way they fight.

My final comment is that with a little practice you can stop a serious dog fight in about 5 seconds, on the average. It's so easy you can't believe it , straddle/grab/break and you're finished! No unnecessary damage due to pulling  beating or whatever else one might employ!

So, the next time you're playing with your dog, open the mouth and you'll see the GAP I mentioned. Then, when you get your 'stick', just play tug-o-war or have the dog grab something and try your breaking stick then.