Many years ago, a Basenji punctured the throat of my much beloved Spaniel/Eskie mix named Juju. I approached the guardian of the Basenji and explained the situation. Not only did she not believe me ("my dog would NEVER do that" were her words), she up and left the dog park. I was left with a dog bleeding from several puncture wounds in her neck and the utter disbelief someone would just leave after their dog bit another.
At another dog park, I and other visitors watched in horror as a Labrador Retriever killed a Yorkshire Terrier. The small dog did not stand a chance against the 80lb dog - his neck was broken almost instantly. The guardian of the Lab gave false information and left the scene immediately, even though no one was attempting to harm either the Retriever or his owner.
Mina was once attacked by a Great Dane mix. The dog tore a quarter-sized chunk out of her head - you can still feel the scar and the hair never grew back properly, it has always been tinted a cream, sometimes pale yellow color. With adrenaline pumping, I managed to drag the dog off of a screaming Mina (it's one of two times I've ever heard Mina scream), even though she weighed more than me. The owners offered their apologies and then walked off. I was stupefied, standing there with a bleeding, trembling dog cradled in my arms...and later, a $500+ vet bill.
I've only been in one situation in which a dog in my custody attacked another. I was dog-sitting and had her at the dog park when a smaller mixed breed dog tried to take her ball. She attacked this dog. While it was over with quickly and no one was seriously harmed, the other dog had a few small puncture wounds. I am not trying to make myself into a holier-than-thou personage, and while it crossed my mind that fleeing would be "easier", it never occurred to me to just leave without first making sure the other dog was okay and then giving out my contact information for any vet bills (there weren't any, thankfully).
Dog fights happen. Dog bites happen.
And when your own dog exhibits normal canine behavior that shocks and horrifies, it is your responsibility to make sure the victim is okay. I got to thinking about this after reading this story. A leashed Great Dane met a leashed English Bulldog. For whatever canine reason, the Great Dane became very aggressive and attacked the Bulldog, picking him up and shaking him by the throat. An English Bulldog is not physically made for such encounters and the dog nearly suffocated and died from stress on the scene.
I can get past the Great Dane's behavior. I think the Bulldogs' owners can, in some small way. After all, dogs fight. Even the most innocuous of dogs may decide one day not to like another dog. This is not unusual or aberrant behavior, no matter how freaked out we are by it. Of course if you have any inkling your dog might not like other dogs, you might consider muzzling or keeping the dog away from them.
But then the Dane's owners just walked away. Walked away from a dog bleeding profusely from the throat, barely breathing, turning purple and blue on the ground. By luck, the Bulldog had both owners present who could pick the dog up and rush him to a vet, but what if it had been one slight person? Someone who couldn't physically lift the 70 lb, bulky dog and get to a vet? That is not an unreasonable "what-if".
To leave a dog bleeding and injured, to abandon a traumatized human and canine alone - that, to me, is unconscionable. I can understand removing the attacking dog from the situation, but the situation in which you have to outright flee is rare. Most of the time, one can work out a way to get contact information to the victim without leaving the scene.
People do strange things, though. I can tell you it would have been easier to walk away from the screaming owner of that small dog, to just get away from the stress and fear she exhibited (far greater than the dog). I know what fear and adrenaline can do - it can inspire normally grounded people to engage in strange, unusual behavior (like flinging a 150 lb dog off a 35 lb dog). It fleetingly crossed my mind to do just that, leave.
Unless you or your dog's life is in danger, never ever leave an injured dog/person alone. It seems like such common sense, but I've seen and read time and time again people doing just the opposite.
And that's my public service announcement of the week.