As per Wikipedia,
Baseball is a bat-and-ball sport played between two teams of nine players. The aim is to score runs by hitting a thrown ball with a bat and touching a series of fourbases arranged at the corners of a 90-foot diamond. Players on the batting teamtake turns hitting against the pitcher of the fielding team, which tries to prevent runs by getting hitters out in any of several ways. A player on the batting team can stop at any of the bases and later advance via a teammate's hit or other means. The teams switch between batting and fielding whenever the fielding team records three outs. One turn at bat for each team constitutes an inning and nine innings make up a professional game. The team with the most runs at the end of the game wins.
Evolving from older bat-and-ball games, an early form of baseball was being played in England by the mid-eighteenth century. This game was brought by immigrants to North America, where the modern version developed. By the late nineteenth century, baseball was widely recognized as the national sport of the United States. Baseball is now popular in North America, parts of Central and South America and the Caribbean, and parts of East Asia.