My pit mix was beaten up a few times as a young pup and I believe this was the cause of his current behavior. When another dog fetches or runs he is more interested in biting the other playing dog. He refuses to listen to commands (though he listens VERY well in controlled situations). He has recently injured another dog with this play (I am convinced it is play) but seems oblivious to any correction I have attempted so far. I fear that if I don't get this corrected, I won't be able to let him play with other dogs at all. He shows almost no other aggressive behavior towards people or dogs. Not even raised hair. Otherwise, he is mild mannered and a very happy pup.