Ask a Vet: Why Are Dogs Aggressive Toward Other Dogs When Off-Leash?


Welcome to our weekly 'Ask a Vet from the SF SPCA' feature on Dr. Jeannine Berger, DVM, DACVB is a board certified veterinary behaviorist who counsels guardians whose pets’ issues are beyond the scope of training. Think of her as a pet shrink…at your service. Ask your own questions in the comments!

Aggression to a certain degree is a normal social and adaptive behavior in virtually all animal species and domestic dogs are no exception. Luckily, there are a number of things you can do to minimize both the frequency and intensity of dog-dog aggression.

Dog-Park Fighting

Dogs can be bullies, protective about toys or food, or socially uncomfortable, and any of these issues can make for regular excitement at the dog park. Dogs don’t automatically get along with every dog they meet, just like we don’t get along with every single person we come across.

Most importantly, keep in mind that dog parks don’t suit every dog. Many dogs thrive on social time with other dogs, but some need their personal space and that’s okay, too. If that’s your dog, bypass the dog park and instead use hiking trails, beaches, or other less-crowded spaces for your dog’s exercise.

What You Can Do

Be honest with yourself: is your dog is truly a good dog-park candidate? Is he socially versed and friendly with dogs of all sizes, breeds, and temperament, and enjoys to play and wrestle?

Here’s what to look out for:

Bullying behavior includes jumping on top of, pinning down, or continually chasing and nipping other dogs. If your dog usually plays well but seems to target certain dogs for bullying, give him a time-out whenever it happens. I.e. leash him up for a couple of minutes or, if he does it again, take him home. It is your responsibility to keep other dogs safe.

Protectiveness of toys. If your dog gets into scuffles over toys, you can manage the problem with good situational awareness. Don’t bring a toy to the park and actively supervise your dog’s playtime. Look out for balls or Frisbees so you can call him away from those before he get them.

Social discomfort. Most problems arise from dog being fearful as they are socially uncomfortable with unfamiliar dogs. These dogs can possibly learn to love the dog park with carefully planned exposure. Take your dog there at times when you know it will be less crowded and keep the sessions short. If your dog ever seems uncomfortable or scared, engage him in some solitary play with a toy and leave the park when he is happy.

In any of these situations: If the behavior continues despite your careful supervision and active management, or your dog gets into serious fights or inflicts real damage, he’s obviously not a dog park candidate and should not be taken to the park.


  • Spay or neuter your dog. This is very important, especially with intact male dogs, who are at higher risk of tangling with other males.
  • Make sure your dog is up-to-date on vaccinations, flea prevention, and deworming treatment.
  • The SF SPCA offers on and off leash classes – check our website for availability
  • If your dog shows aggression towards unfamiliar dogs and can’t take a class and your own efforts aren’t successful, we recommend contact SF SPCA’s board-certified veterinary behaviorist. Don’t live in the Bay Area? Search locally for a veterinary behaviorist (Dip ACVB), a Certified Applied Animal Behaviorist (CAAB or ACAAB), or a Certified Professional Dog Trainer (CPDT)
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