If a dog was attacking a cat, I would do whatever I could to save the kitty or make the bites/injuries less severe. I lived next door to an aggressive chihuahua many years ago, he was always running loose in the front of the owner's house, and whenever anyone tried to walk on the sidewalk, or when I got out of my car to go into my house, he would charge at me growling and bearing his teeth. The owner would always appear after the fact and say sorry. Luckily he never bit me, but the owner himself said the dog bit him numerous times.

Now there's a Chihuahua mix across the street that gets loose once in awhile, and seems to be the same way. I've seen a couple over the years that were well socialized at the park, but I've also seen some in stores with people who tell others, don't pet him he might bite. Never trusted them just from what I've seen.