Cats are not usually very protective with trying to defend their owners when they are being attacked but they are very good at defending their kittens or other animals like chickens they love.
Have you witnessed a cat defending and fighting for another animal?
Yes, I have seen it multiple times. I've seen a cat defending a puppy from an aggressive mother dog. I don't know why the dog was getting angry at the little puppy but the cat stood it's ground and take the puppy away from there until the dog calm down.
I haven't seen a protective cat before. Cats are animals that live on their own and they won't even care about what's going on in your life. Their own is to be feed when they are hungry or thirsty.
A mother's love is existent in almost every living thing and cats are not exempted from having this trait. I've seen cats fight snakes and other bigger animals like dogs and bigger cats trying to harm their kittens.