A horse?! that guy is delusional... most men won't have the ability to defeat (unarmed) anything bigger than a medium size dog...
Anything bigger will likely overpower a regular human, most smaller would just be too fast or have different, naturally occurring weaponry to defeat us
Well, if somebody poses aggressively in front of you randomly on the street, the wise thing to do for you would be to run away. You could probably overpower them, but it just isn't worth the risk most of the time.
Yeah horse messengers were only really a thing when you could change horses at stations. That's the whole point of the marathon. It's based on the history of a foot messenger (at a time when we very much had domesticated horses).
Assuming both sides see it as a fight to the death, the horse will also engage so you could just run away into a bunch of traps. All you need is for the horse to injure a leg in one trap and it's done for. I think even just some holes with a couple spikes would be enough to injure and maybe even sprain an ankle.
Without prep time you're pretty doomed, I think your best bet is either climbing up a tree to buy you some prep time to make a spear out of the branches or worst case diving in, aiming to do damage to its legs (unlikely) and hope you are able to get out without being trampled (unlikely)
I imagined this question as in a boxing ring/cage style fight.... if planning is involved, I can say I have killed thousands of cattle and even more large hogs just by participating in buying their meat at the grocery store
Yup. Humans aren't large animals. If you want to compare bodysize, check the weights of the animals and the heights of everyone on all fours. Humans are mid.