I have the same problem with my dog, though she only shows aggression towards other dogs. Someone called it fear aggression. When we walk past another dog, she growls, barks, and pulls so hard she almost rips my arm off. Her fur on the back of her neck stands so far up, I would sware she has some shark in her. lol Once she gets near enough to do something, she instantly turns into a scared dog. She has a puppy who seems to be picking up the same bad habit.

I'm taking my dog to the humain society where I got her. They are going to give her an aggression test and then we will go from there. I'm hoping I can get her into a class with dogs with similar problems. This way I can socialize her with other dogs, and I don't have to worry about other people in the class, because they are having the same problems as me.