I work at an animal shelter as a behavioralist and have a lot of interactions with animal control on situations like this.
So it will depend on your state if you live within the US.
In my state, the owner is at fault as the dog is not on the owners property.
Stand your ground laws are in effect that you are able to defend your person and your property (in my state, a dog is considered property) from the dog. This means you are within reason to kill the dog if you preceive the dog to be a deadly threat to yourself, your dog, or your family.
That being said, you should use your best judgement to determine that outcome. I'd never suggest killing a dog if you do not feel like it's the only option.
Dog fights are difficult situations. Never stick your hand in the middle of the fight. Your own dog may even bite you as a redirection.
Pulling the legs out from behind the other dog is a way to stop the fight, but may only be a temporary solution. In addition the dog may try to attack you. If you where to use this method, I'd suggest learning about it and being aware of the dangers before doing it in practice.
If this is something you are worried about, I'd suggest carrying a dog deterant. This can be either a mace-like deterant or compressed air (cold and loud). They sell these as pocket sized as well as large cans.
This post was edited by The_Chosen on Jul 10 2021 03:50pm