Here's where we get into some serious debate about the date of baseball's invention. Some cite the first reference to baseball as a 1744 book called "A Little Pretty Pocket-Book." (Not exactly where you'd expect to find a baseball tutorial these days.) Also in the book is the first mention of a game called rounders, which bears a similarity to the modern baseball game.
We can't be sure which one was first, but rounders does seem to be a simpler version of baseball. A pitcher throws a ball (like a wide strike zone, it must be under the head and over the knee of the batter) to a batter holding a stick-like bat. No matter whether or not the batter hits the ball, he or she must run an irregular shaped pentagon of four posts, staying at any post. The batter is out if a pop-up is caught by any of the fielders, the ball touches the post the batter is running to, or a fielder holding the ball touches him or her.
Sound familiar? Well, also consider that nine people constitute a side and that three bad balls (not in the "strike zone") mean half a rounder for the runner, much like a walk in baseball. Whatever came first, it's probable that baseball and rounders borrowed liberally from each other.