go to this site but you really need to get your dog in training before that behavior gets even more agressive and bigger http://www.pitbulllovers.com/training-articles/pitbull-puppy-training.html

Well my first guess is to get rid of him right away. First thing he is a pittbull. They don't have a good rep. Puupies who do that is naturaly aggressive and cannot be trusted. Do not take the chance. i speak from experience. Who do you love more? Do not take the chance. I did and I have regreted it ever sinse.

Start by learning what games get him wound up and avoid those...when he starts to get too wound up STOP THE GAME. This is what his mother would do, and it sends a clear signal to any puppy that the behavior is not acceptable..starts to nip and get out of control.....GAME ENDS. When he starts to grab with his mouth as all puppies do, replace your body part with an acceptable toy, if he won't take it...GAME OVER. Ignore him. This is common behavior for almost all puppies, as they attempt to learn WHO is in charge here, and what acceptable play consists of. This is NOT a pit bull trait only...almost all puppies go through this stage...part of it reflects their age when they were removed from their Mother and Siblings...the longer they had with Mom, the less rambunctious they tend to be, because Mom taught them some healthy limits! This little fellow is also at the perfect age to start training..the more often you train (about 10 minutes at a pop, but you could train 2 or 3 times a day)...the better he will become at doing good, acceptable behaviors! In reality, almost every interaction is a training opportunity. For Example, my dogs never get a treat or fed without DOING SOMETHING...come, sit, sit QUIETLY...they do a behavior and receive a reward for doing it....when I call them, they are rewarded with loving attention and petting...as long as they are standing quietly, or sitting...they often just sit without being asked, because they KNOW that desired attention comes with sitting quietly... Always remember to set your dog up for success at doing what ever it is that you want the dog to do...then reward for good behaviors... Most Pit Bulls are extremely devoted to their families, and in reality are often amongst the most tolerant dogs towards children. Many have issues and challenges with other ANIMALS, but I've seen rather a good number that were 100% loving towards other dogs and cats too. It's always good to socialize young dogs and puppies of all breeds and to be aware of your dog's level of prey drive.

This is a huge problem and the dog won't change. What will you do when the dog loses control? Too big a risk.