Basketball is one of the few sports whose exact origin is definitely known. In the winter of 1891–1892, Dr. James Naismith, an instructor in the YMCA Training College (now Springfield College) at Springfield, Mass., deliberately invented the game of basketball in order to provide indoor exercise and competition for the students between the closing of the football season and the opening of the baseball season. He affixed peach baskets overhead on the walls at opposite ends of the gymnasium and organized teams to play his new game in which the purpose was to toss an association (soccer) ball into one basket and prevent the opponents from tossing the ball into the other basket. Because Dr. Naismith had eighteen available players when he invented the game, the first rule was: “There shall be nine players on each side.” Later the number of players became optional, depending upon the size of the available court, but the five-player standard was adopted when the game spread over the country. U.S. soldiers brought basketball to Europe in World War I, and it soon became a worldwide sport.