The remainder of this article contains lore created collaboratively by the Blaseball community.
Horses are a species of creature native to the planet Earth. In relation to blaseball they are not allowed, and in fact, it is illegal to have a horse at a blaseball game or invite one into a blaseball stadium. The reason for this is cited in the final chapter of the Book of Blaseball and relates to the events of opening the Forbidden Book. Horses, being mostly comprised of multudinous gasses are unable to appreciate Blaseball, cannot comprehend integral statistics of splorts, and are impossible to control when exposed to a Blaseball pitch.
Horses are the only entity currently capable of chewing Gum and are immune to the Gum Curse, so they may appreciate some aspects of blaseball.
While Horses are not allowed in blaseball, Hlorses are, and in fact, a few players in the league are Hlorses. Summers Pony is allowed to play because they identify as a pony, not as a horse. Sexton Wheerer of the Unlimited Tacos is a unique case, being a horse-torsoed centaur.