Most people are going to fight back with every last ounce of strength they have
What about a horse? Should I not stand behind it or something? What other precautions should I take?
I don't know how much experience you have with horses, but they are large and exceptionally powerful creatures. We don't use the term "horse power" for nothing. Think of them as large dogs with hooves. As soon as you start getting aggressive with it, it's going to start bucking, kicking, neighing - possibly screaming (I don't know if you've ever heard a horse scream) - and biting.
Let me put it to you this way - if I was going to bet on a single human versus a single horse in hand to hand combat, I'd put my money on the horse every time. They can literally tear your face off with a single bite. They can shatter your ribcage and/or skull with a single kick. It's not going to be something you can do quietly.
Your best bet would be to club it over the head with a sledge hammer or something. Even that isn't a guarantee, since if you don't kill it with one blow (and, you may not - they have tough skulls) all hell is going to break loose.