ok so when it comes to play. dogs when play fighting can sometimes get out of hand like that. they get over stimulated and switch from play to fight. penning her up most likely wont help . when dogs play they normally take turns being the "dominate one". you will see them take turns. one will be the one pinned on the ground then he will pin the other to the ground and so on. this is fine and well when you have two dogs that are well socialized and have learned how to play properly this doesnt turn into a full blown fight. there's two possibilities here. one you have to take into count the fact your dog is still very young. puppy's are not born knowing how to play the right way. its something they have to learn. when the other dog "starts winning the fight" (pinning him down or putting his paw on his back) your dog may be seeing it as him trying to dominate him. so he goes from "hey this is fun" to "oh hell no i dont think so". if your watch them closely you can see when the play starts to change and then you can stop it before a attack happens. if a attack does happen though there are a few things you should do. if he is the only one attacking then you should pin him to the ground using your hand to act like a dogs jaw on the side of his nack and firmly ( not too hard) hold him to the ground. then you should bring over the dog that got attacked and him have camly sit right beside the attacking dog as you have him pinned to the ground. now let me explain. when he was with his mother and played too rough with her she would take her jaws and pin him to the ground to "punish" him. this taught him limits when playing. this is all natural and its a language that a dog understands. the point in bring the other dog over is becuase if you leave it be and just punish the attack the one who was attacked will become scared of him and possibly other dogs as well. when you pin the attacker to the ground your making him submit. the other dog sees this and sees you are in control and it helps make him feel better. the point in bring him over while the attack is pinned is becuase you then make the one that was attacked the dominate one. and it shows him that its ok to be around him again. some dogs are just born more dominate then other dogs. for example. my pitbull lab mix will let my other dogs push her off her food bowl. now if my other dogs tried that with my peekehund she would snap at them and let them know "hey this is my bowl leave me alone" as you can ... (more)