Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. William M. Day (1867-1923), was a Major League Baseball pitcher who played in 1889 and 1890 with the Philadelphia Quakers/Phillies and the Pittsburgh Alleghenys. He was still playing professionally in the minor leagues through 1904. Major League Baseball (MLB) is the highest level of professional baseball in the United States and Canada, consisting of teams that play in the National League and the American League. The two leagues merged in 2000 into a single MLB organization led by the Commissioner of Baseball after 100 years as separate legal entities.