Horseshoes
In the wild, horses don't wear shoes and have little if any protection for their feet. They run over wilder terrain than their domesticated cousins, which may beg the question as to why we need to shoe domestic horses. Comparatively, wild horses move more slowly and rarely need to run--and thus rarely need to worry about their feet. Evidence exists of prehistoric horseshoes, more like booties made out of animal hide and plant fibers. These slowly evolved into the Roman "hipposandals," literally sandals made for horses, with leather straps and metal buckles. It wasn't until the sixth century that the shoes were nailed to the hooves, meaning the original horseshoes for the sport looked very different from those we see today.
Discus Throwing
A predecessor to the sport of horseshoe throwing was an event now associated less with backyard sports and more with track and field. A discus is a large, round and heavy weight that is about 10 to 12 inches in diameter. What Greek soldiers did, and modern athletes do, with this object is grab it and try to throw it as far as they can. It's a competition not of precision (like horseshoes) but of strength and distance.
Quoits
No one is exactly certain which game came first: quoits or horseshoes, but both are considered contemporary games. Some ancient Greek armies that couldn't afford a discus would instead set up stakes and throw either discarded horseshoes or large metal rings--sometimes formed from discarded horseshoes--at them. Bent horseshoes were intended to evoke the chakram, a bladed, ring-shaped weapon. This sport became known as quoits and is still around today, although it is slightly less famous than its contemporary counterpart.
Horseshoe Throwing
Like quoits, horseshoes is a sport that evolved first from idle armies, where soldiers would have a friendly throwing competition, using either a discarded horseshoe or the ring formed from one. At first, it was about distance: The strongest soldier, the one who could throw the object farthest, won. Later, however, distance wasn't the issue and precision was the new goal. Stakes were set up, and soldiers took turns throwing the object at those stakes.
Rules
The idle pastime of tossing objects at a stake passed on through centuries, even through the American Revolutionary War. By this time, discarded horseshoes were less common, but the sport was still popular enough for people to get ideas when they found a horseshoe. It was about 1869 when rules were first set down for horseshoes. The rules dictated that the stakes be 19 yards across, horseshoes should be no more than 8 inches wide and the pitcher has to throw on his first step. The National Horseshoe Pitchers Association of America was formed in 1925 and continues governing games and tournaments.