Some of the signs of dogs happily playing include growling, nipping with their teeth, and rolling around on the ground. Some of the signs of dogs getting aggressive and fighting with each other are—well, they can be the same! It can take some additional clues including understanding dog body language to know whether your dogs have crossed the line from play into fighting behavior. Here's a guide to knowing whether your dogs are playing or fighting.
The website of the American Kennel Club says that the growling, snarling, body-slamming, and neck-biting that puppies often do is normal puppy play behavior. As soon as they open their eyes, puppies start wrestling with each other. It's the best way for them to learn socialization, as well as how not to bite too hard. If a puppy play-bites another puppy and that puppy yelps, the first puppy learns that his bite was too hard, which is a valuable lesson going forward.
So what do happy, playful puppies look like? Happy puppies will put their front end down and their back end in the air. Puppies who are growling may sound more serious than they actually are, and it can seem sustained and exaggerated. The dogs "fall down" repeatedly and expose their bellies. Sometimes you can even tell they are "grinning" while they are doing all these things.
Dogs are social animals, and play behavior is how they learn how to interact with other dogs. You can think of social play in puppies as role-playing rehearsals for how they will act as adult dogs. Most dogs could easily bite hard and hurt people and other dogs, but they learn not to. It's common for dogs to get territorial over food and toys, so keeping those items out of the picture could limit the dog's desire to fight.
The AKC website says even in play, it's not ok for dogs to gang up on other dogs. Even if this doesn't lead to being hurt, it can be an experience that limits your dog's ability to interact with other dogs in a healthy way in the future. If it looks like one dog has had enough and wants to stop, but the other dog keeps going, it is probably time to separate them. It can be easier to do this if you give them a distraction.
Adult dogs will exhibit many of the same play behaviors as puppies. But of course, there's more power behind them, so if they do turn aggressive, it can turn into a problem quickly. Hills Pet says it's common for both puppies and adult dogs to bite, but it's not a problem as long as aggressive growling, yelps, or whimpers don't go along with it.
Hills Pet says signs of dog aggression include raised hackles, stiffness, snapping, or lunging. If you see these signs, separate the dogs immediately. But be careful! Never put yourself in between two fighting dogs, as you could inadvertently be bitten.
The importance of play
Dog trainer Andrea Arden says that when puppies have consistent interactions with other dogs as they grow, it provides them with valuable information in regards to how forcefully they bite. It's also an important form of socialization in that it gets them used to being around other dogs (that leads to many happy hours at the dog park!). Arden says allowing dogs the opportunity to play with other dogs during their crucial development period of 26 weeks and younger is one of the easiest and most effective ways to encourage healthy interaction with other dogs throughout their lives.