In Major League Baseball, there have been interleague rivalries. These rivalries have been due to the frequency the teams have met and the geographic proximity (both teams are in the same city, but in different leagues). Before interleague play began in 1997, the only time such matchups have happened was in the World Series.
Early discussions about interleague play
Interleague or interconference matchups have long been the norm in other professional sports leagues such as the NFL. Regular season interleague play was discussed for baseball's major leagues as early as the 1930s. In December 1956, Major League owners considered a proposal by Cleveland general manager and minority-owner Hank Greenberg to implement limited interleague play beginning in 1958. Under Greenberg's proposal, each team would continue to play 154-games in the season, 126 of which would be within the league, and 28 against the eight clubs. The interleague games would all be played during a period immediately following the All-Star Game. Notably, under Greenberg's proposal, all results would count in regular season game standings and league statistics. While this proposal was not adopted, the current system shares many elements. Bill Veeck predicted in 1963 that Major League Baseball would someday have Interleague play. The concept did not take hold until the 1990s (at least in part as an effort to renew the public's interest in MLB following the 1994 players' strike).
First Interleague games
MLB's first regular season interleague game took place on June 12, 1997, as the Texas Rangers hosted the San Francisco Giants at The Ballpark in Arlington. There were four interleague games on the schedule that night, but the other three were played on the West Coast, so the Giants–Rangers matchup started a few hours earlier than the others. Texas' Darren Oliver threw the game's first pitch and San Francisco outfielder Glenallen Hill was the first designated hitter used in a regular-season game by a National League team. San Francisco's Stan Javier hit the first home run in interleague play, and the Giants won the game, 4-3.
From 1998 to 2001, teams from the American League West played teams from the National League West, etc., typically scheduled to alternate between home and away in consecutive years. However, in 2002, the league began alternating which divisions played which divisions, and thus in 2002 the American League East played the National League West, the American League Central played the National League East, and the American League West played the National League Central. Matchups which had been of particular interest prior to this format—mainly geographic rivals—were preserved. This is expected to be the continuing format of the interleague schedule. Corresponding divisions however, were skipped once when this rotation began, but were put back in the rotation in 2006.
Since 2002, all interleague games have been played prior to the All-Star Game. Most games are played in June, though May games have been scheduled since 2005.