 The Arizona Diamondbacks of Major League Baseball (National League West Division) began play as an expansion team in 1998.With their arrival in the valley, Phoenix became just the 10th city in the nation to host a major league team in all four major sports.The team has played all of its home games in the same downtown park; originally called Bank One Ballpark (or "BOB" for short), in 2005 the stadium's name was changed to Chase Field.