The following question has been bouncing around the Internet for a while now, and somebody finally got around to asking me for my opinion:
Which would you rather fight - 100 duck-sized horses or 1 horse-sized duck?
Honestly, I wish I had been asked sooner because there seems to be a lot of debate on this topic but the answer is obvious.
In the spirit of the question, I am going to assume that the battle will take place in reasonably open ground, with objects that can be used as makeshift weapons (cudgel-ready branches, etc). I am specifically thinking of that episode of Star Trek where Kirk is forced to fight that lizard man although I probably wont be able to make any gunpowder.
Anyway, given the above premise I would chose to fight the 100 duck-sized horses any day of the week.
Now a full sized horse is a formidable beast. They can bite and a proper kick from a horse can kill a human, but horses are not built for combat. Their mouths are made for cutting and grinding grass, and they lack claws. I doubt a kick from a tiny horse would leave much of a bruise. Perhaps they could give you a nasty nip with the front incisors, but I don't plan on letting any of the horses get that close.
Lets talk about energy requirements. In general, large animals tend to have lower relative energy needs than small animals. Horses, being completely herbivorous, have fairly good stamina compared to most animals but require vast quantities of food. A small horse would spend more time eating and would tire very easily compared to a human.
My plan for winning involves letting the horses tire themselves out by bravely running away. Thoroughbred horses (say 2.6m in length) can run at about 50kph for short distances, a duck-sized horse (say 50cm long) would be much slower and be exhausted after a very short gallop. I am not saying it would be easy but I think I could take on 100 exhausted animals that weight 1/10th of me, particularly if I could separate the herd into smaller groups.
In contrast, a horse-sized duck would be a fearsome sight. Ducks are fairly aggressive creatures and although they also lack natural weapons, they do have spiny feet and a hard beak that could tear into anything man sized. Ducks are also covered in feathers which would deflect or cushion any blow I could hope to land.
Additionally, there exist horses that are quite small if not quite duck-sized. They do not look that tough to me. On the other hand, there used to be horse-sized ducks. They were called dinosaurs and they looked nigh-unstoppable.
In conclusion, this is a very silly question.