Sarah Wilson

Dog Expert

5 Causes of Leash Aggression Toward Other Dogs


Understanding leash aggressionLeash aggression – pulling, lunging, barking at other dogs  – is a common and frequently misunderstood/misinterpreted behavior. It is a rare thing, in my work, that a dog actually wants to cause serious and immediate harm to another dog. In most cases, something else is the root cause of bad on leash reactions.

Understanding what is going on allows you to tailor an effective response that will be helpful rather than making matters worse or setting your dog (and you) up for failure.*

Here we go:


Dogs who are hurting don’t want to be hurt more. Imagine how you would feel if your knee was injured then some young, high energy kid came racing at you.

Clues: Your dog “used to be great” with other dogs and now is grumpy; your dog is good with low-energy, “polite” dogs but snarls and lunges at the exuberant ones; your dog is better at the beginning of a walk than at the end (or vice versa). This is another reason why certain breeds prone to orthopedic problems dislike rambunctious dogs.

Course of action: Talk to your veterinarian or canine PT pro to discover what’s going on; try a course of pain relief and see if the behavior improves; protect your dog from other dogs; skip the dog park; no more hard games of fetch or flying disc until your dog is healed up. If the dog is arthritic, I start joint and fatty acid supplements with the vet’s okay.


Bad experiences on leash can create a “best defense is a strong offense” approach. Major causes of fear on leash are, in no particular order: size differential, previous “training”, previous attack, poor early socialization.

Clues: Your dog is tiny, your dog was less leash aggressive before” training” started, before he was attacked or your dog is a rescue with a history of limited socialization and/or isolation and/or group living conditions like hoarding.

Course of action: Not all dogs “want to say Hi” and I do not expect them to. What I ask of dogs is that they walk on a loose leash next to me. It is my job to reward that and to protect them, as much as I can, from dogs or situations that frighten them.

Over time, as their faith in me increases and they get more experience not being overwhelmed, we can consider whether we want to address those fears more directly but in many cases, a happy dog walking on a slack leash is plenty for everyone.


Some dogs bark, slaver, stand up pulling against the leash from pure excitement. The barking is rapid and high pitched. Teeth are not flashing and often ears back/tail wagging is going on.

Clues: Dog sees other dogs and loses his mind. Leaps up and down, barks, pulls and in every way attempts to get to the other dog. I see this a lot in some daycare dogs.

Course of action: Work your head turns. Develop his self-control “muscles”. Use these distractions to work games such as Catch My Drift and Mother May I. You want to teach your dog that self-control = chances to greet; not that being out-of-control does.


This is a pretty rare cause but I mention it here because I always find it interesting. This is the category for the “what the heck is THAT” moment where a dog who has never seen (or heard) a pug wheezing his way down the street, or who doesn’t recognize a good canine buddy after a grooming or thinks a tiny toy dog might be some sort of squirrel.

Clues: Your dog is social with other dogs but reacts to one who is new to him (or appears new). Major variation in size – a toy breed or a giant one, movement – waddles like a pekingese or hops like a three-legged one, sound – the wheezing of a short-nosed dog, new look – buddy dog acting all chummy but your dog doesn’t recognize him by sight or smell after a grooming can all trigger some dogs to lunge first and ask questions later.

Course of Action: Any time your dog acts radically different on leash, pay attention! To me, most on leash issues boil down to “the dog is not being attentive to the human” and I focus teaching the dog that distraction = attention. When you have control over your dog’s brain, you have control.


This reason is last because it is most rare and the most serious. Your dog targets other dogs because he wants to hurt them. He may bark ferociously – standing his ground or leaning forward. This is a deep bark. His teeth flash as he barks. He wants to move forward. His tail is stiff behind him or raised straight up. Or, he may silently stare dropping his head slightly in direct alignment with the other dog (which could be play in some dogs, you have to read the whole picture). He may stalk other dogs. He may rise up getting as tall as he can.

If you think your dog might be one of these dogs or if your dog has harmed another dog, please seek qualified professional assistance immediately – this is not a DIY project.

Straight talk: Your attachment to your dog does not trump my attachment to mine. You cannot walk a dog in public who wants to seriously harm other dogs any more than you can walk down the street pointing loaded weapons at the rest of us. If a momentary mistake on your part means my dog could be injured or killed, then your dog is not a “pet” and you cannot act as if he is.

Clues: Your dog scares you. Your dog scares others. Your dog has broken away from you and hurt attacked another dog.

Course of action: Get help! Teach this dog to mind his own business and focus on you. A dog who is focused on you is not attacking other animals. Use a head halter that both gives you control over your dog’s head and closes his mouth when snugged up. It can also inhibit some dogs which is a useful feature here. Do not attempt to socialize this dog on your own as you can make matters worse for your dog and end up hurting/frightening someone else’s beloved companion.

Now you know.

* Note: Use a regular 4’Do not use a retractable leash! They are, at best, counterproductive and, at worst, dangerous for you, your dog and others around you!

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  1. I like this list, however I don’t know that I’d use the word “rare” for the last one. While yes, many of the other reasons are more common reasons for a dog to be reactive on the leash — I find personally that most dogs are this way due to leash corrections on a leash — but being flat out aggressive and wanting to hurt another dog isn’t “rare”. It’s less common but not rare.

    • Hi Stacy –

      So much of our opinion is based on the population we happen to work with and attract. For me, in my work, it is rare here in suburbia. In your area, it may not be so rare or the people who seek you out are ones with more serious issues so it isn’t rare for that reason.

      Glad they have you to help them. Thanks for the comment. Sarah

    • True dog-dog aggression, I mean uninterruptible drive with intention to harm, is indeed very rare, even in the urban setting that I live in. It’s not created by leash corrections, those dogs are majorly wired wrong and are dangerous. Most of the dogs that I work with that have bitten another dog have a combination of fear, poor social skills, and little bite inhibition.

      Even Aimee Sadler, the pioneer of shelter dog play groups, has only come across a few and she travels the country working with shelters.

      So yes, I would agree that true dog-dog aggression is rare.

  2. Thanks Sarah, great article! What should you do if they only seem to show aggression in front of their own house? Normally Polly loves to see other dogs, but if they walk past our house, even if it is on the other side of the street, she starts barking, growling, the hair on her back stands up and she starts kicking dirt. She does this with joggers and kids on bikes too, again only in front of our house.

  3. Thanks for a great blog post on a topic very close to me. As a NYC dog walker, on leash aggression is all too common, unfortunately. Hopefully, your post will educate. Love the note at the end about NOT using a flexi leash!!

  4. I liked this article a lot too. You might also add ‘previous aversive methods of training around other dogs’ to the list!

    • Hi Karen – Glad you liked this one, too. I’m on a roll! 😉

      Covered training issues under: “Major causes of fear on leash are, in no particular order: size differential, previous “training”, previous attack, poor early socialization.”

      So, I hear you! Sarah

  5. Thank you for this excellent post. There’s one small thing in it which is rubbing me the wrong way. I do not think that a truly aggressive dog, loved by its owner, is any less a pet than any other dog. I think there might be a better way to express what you meant.

    • Ingrid, when a person’s child turns out to be a child molester or serial killer or whatever, it makes them no less that person’s parent, but the deviant does not stay in society just because they are loved at home for who they are.

  6. I have a pit bull that is aggressive when on a lead. I have taken him to a trainer and she explained that when he is on lead, he feels the need to protect me. But if he is off lead (which she did in a controlled environment, he was fine with other dogs – although he can be a bit pushy). She explained to me that it is not necessary for all dogs to go up to each other, sniff and be friendly. I can walk him but need to keep him away from other dogs when on lead. I am able to control him, I just always tried to greet others and he would have none of it.

    • Rae, one of the things I get to tell clients quite a bit, and it shocks them often, is that all dogs aren’t going to like all other dogs. And that’s just fine. I think most people just assume that dogs, being social creatures, should just automatically love the company of their own kind.

      Humans are a social species, too. But do you know anyone who automatically loves all other people? I don’t.

      My goal is to make sure my clients who have dogs who would prefer not to meet most other dogs have excellent control of their dogs and are not continually subjecting them to “he just wants to say ‘hi!'” situations. It sounds like you “get” this.

      It’s hard for the owners of truly outgoing, nondiscriminating dogs to understand this until they’ve owned a more discriminating dog. 😉

  7. I don’t have money for a trainer and I already practice all of the diversionary tactics most suggest. Stll,my dog barks and lunges at other dogs on the leash and trust me, its pretty scary. will any of the halters help

    • Hi Sue –

      “Diversionary”? What have you been taught to do? At what point does your dog launch? What breed/mix is your dog? Yes, a halter may help because controlling the head itself makes a big difference. – Sarah

  8. Hello. This may be long. Beagle/Bassett mix; rural stray rescue at 1.5 yrs. that had never entered a house. She was not housebroken so I took her everywhere with me the first 6 mo after rescue. She was a breeze (except for the house breaking thing; which we finally worked out). I could take her anywhere with kids or dogs and she was very well mannered.

    Moved 6 months post rescue and continued the same routine. About a month post move she started barking and lunging at other dogs on our normal walks to and from school; dogs she may have calmly and playfully engaged with just the day before. Also my dad died during this time. I had a GSD prior to her that also had dog leash aggression despite early socialization which I successfully curbed with distraction at immediate interest and also old age helped to mellow (found out later his parents were very dog aggresive).

    I get the psych behind this: change, handler (me) stress and probably I panicked when she exhibited similar behaviors to my GSD. We have sought out a trainer but cannot work past the leash-based dog aggression. I did obedience and rally with my shepherd so I have some training experience but am struggling here. She has come so far and I see how much she has grown since having a home but we struggle in this area. A strange dog can enter her home and eat her food; play with her toys, she plays with them and enjoys it; excellent at dog park, wonderful off leash with other dogs and with recall and great at doggy daycare. On a walk though she lunges and acts like a crazy dog.

    It has become a cycle; I stress when we see a dog, she reacts. I get what is going on but not why it is so extreme nor how to break the cycle!?

    • Never mind the aggression right now, focus on your basics. How are her head turns and simple sits? Whenever something isn’t working, it usually means the fundamentals need work. And work you do in home or in your driveway leads to better control in stressful situations. I don’t know what you’ve done or what tools you are using but I do know it CAN be changed (not that she will like dogs but she won’t fire at them).

      I would ask “When did you start daycare?” Daycare can start this sort of thing if it isn’t well supervised or planned and very few of them are. Anyway, work your basics. Good luck!

  9. Hi,

    I have leash aggression with my 2 year old Border Collie. Bought him from an original owner. He does great socially at the dog park except when younger dogs bother him for too long and try to steal his Frisbee. When walking him on a leash he starts barking or getting down on the ground like he is getting ready to attack when seeing another dog, even puppies. Any suggestions?

    • Hi Mike – Yes, start teaching him head turns (Look At Me in My Smart Puppy) and blocking. Organize his time at home so listening to you is a habit. BC are sensitive and smart; we either use that for good or they use it in ways that they cannot help. We need to help them. Good luck – Sarah

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