Interleague play is the practice of regular season Major League Baseball games played between teams in different leagues. Before being introduced in the 1997 season, matchups between teams in the American League and National League only occurred during spring training, the All-Star Game, other exhibition games such as the Hall of Fame Game in Cooperstown, New York, and the World Series. Unlike modern interleague play, none of these contests, except for the World Series, counted toward official team or league records.
Early discussions 
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 a 154-game season, with 126 within that team's league, and 28 against the eight clubs in the other league. The interleague games would be played 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. While the concept was again considered in the 1970s, it was not implemented until the 1990s, at least in part as an effort to renew the public's interest in MLB following the 1994 players' strike.
Interleague play introduced 
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 1997 to 2001, teams from the American League West played teams from the National League West, teams from the American League Central played teams from the National League Central, and so on, 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 were skipped once when this rotation began, but were put back in the rotation in 2006.
From 2002 to 2012, all interleague games were played prior to the All-Star Game. Most games were played in June, though May games were scheduled after 2005.
The designated hitter (DH) rule is applied in the same manner as in the World Series (and the All-Star Game prior to 2010). In an American League ballpark, both teams have the option to use a DH. In a National League ballpark, both teams' pitchers must bat. Some baseball observers[who?] feel it might be fairer to reverse this (in other words, always follow the DH rule of the visiting team instead of the home team), thereby offsetting the home-field advantage as well as exposing the fans of the home team to the other league's rules. Teams from both leagues have both benefited and have been at a disadvantage when it comes to the DH rule in interleague play. For instance, Barry Bonds, who spent his entire career in the National League and actually won eight Gold Gloves earlier in his career, was used strictly as a DH later in his career when the San Francisco Giants played away interleague games due to his poor fielding. Conversely, Boston Red Sox slugger David Ortiz, who to date has spent his entire career in the American League and is the Red Sox's regular DH, is forced to play first base when the Red Sox have away interleague games, forcing the Sox to give up good defensive fielding in favor of Ortiz's power hitting.
After the 2010 interleague play, the American League holds an all-time series advantage of 1,808–1,652 and has finished with the better record in interleague play for 7 straight seasons, dating back to 2004. 2006 was the most lopsided season in interleague history, with American League teams posting a 154–98 record against their National League counterparts. The team with the best all-time record in interleague play is the New York Yankees of the AL at 144–102 (.585), followed by the Chicago White Sox at 143–104 (.579). The Miami Marlins holds the NL's best interleague record at 127–107 (.543), followed by the St. Louis Cardinals at 109–96 (.532).
In 2007, two teams—the Los Angeles Dodgers and the Baltimore Orioles played 6 games with more than one interleague opponent. The former playing both the Toronto Blue Jays and the Los Angeles Angels of Anaheim while the latter played both the Arizona Diamondbacks and the Washington Nationals. This happened again in 2012 as the New York Yankees played both the New York Mets and the Atlanta Braves for 6 games. The Miami Marlins also did this, playing both the Tampa Bay Rays and Boston Red Sox for 6 games each.
The first Civil Rights Game was an exhibition interleague game between the Cleveland Indians and St. Louis Cardinals in AutoZone Park on March 31, 2007. The first regular season Civil Rights Game was an interleague game between the Chicago White Sox and Cincinnati Reds in Great American Ball Park on June 20, 2009.
Wins by league 
|Year||Best Record||Total Games||American League||National League||Winning Pct.|
Interleague wins for 2013 season as of April 30.
The total number of interleague games scheduled for each season from 2013 is 300. (20 games per team * 30 teams / 2 teams in each game)
Interleague statistics 
The following is text of Major League Baseball's policy regarding the compilation of statistics as a result of Interleague Play:
"For the first time in the history of Major League Baseball, Interleague games are to be played during the regular season. Breaking tradition always brings about controversy and the matter of baseball records is no exception.
"It is the opinion of Major League Baseball that there is no justification for compiling a new volume of records based on Interleague Play. On the contrary, the sovereignty of each league's records will be retained, and if a player or a team breaks a record against an Interleague opponent it will be considered a record in that league. In cases where two teams – as Interleague opponents – break a league or Major League record, that record will be annotated with the phrase 'Interleague game.' Streaks by both teams and individual will continue (or be halted) when playing Interleague opponents in the same manner as if playing against an intraleague opponent. In essence, records will be defined by who made them rather than against whom they were made.
"The official statistics of both leagues will be kept separately as they have in the past. This means statistics for each team and their individual players will reflect their performance in games within the league and also in Interleague games without differentiation."
Interleague-play leaders 
- Batting Average (min. 300 at-bats)
- Home Runs
- Runs Batted In
- Wins (by pitcher)
- ERA (min. 100 innings)
- Year-by-year Stats
Geographical matchups / Natural Rivals 
Several interleague matchups are especially anticipated because of the relative proximity of the teams involved. In the case of each of these "rivalry" matchups, the two teams play four games (two home games and two away games) against each other every year:
- Baltimore Orioles v. Washington Nationals (Beltway Series)
- Chicago Cubs v. Chicago White Sox (Windy City Series, Crosstown Classic, BP Cup, or Red Line Series)
- Cincinnati Reds v. Cleveland Indians (Ohio Cup)
- Detroit Tigers v. Pittsburgh Pirates
- Kansas City Royals v. St. Louis Cardinals (I-70 Series or Show-Me Series)
- Los Angeles Angels of Anaheim v. Los Angeles Dodgers (Freeway Series)
- Tampa Bay Rays v. Miami Marlins (Citrus Series) (also the "Marine Biologist" and "Sunshine" Series)
- Milwaukee Brewers v. Minnesota Twins
- The Twins and the Brewers were formerly regional rivals in the American League, dating from the Brewers' relocation from Seattle after the 1969 season until the team's realignment into the NL Central for the 1998 season. The two metro areas are connected by Interstate 94. However, the term "I-94 Series" is used almost exclusively to refer to the games played between the Milwaukee Brewers and the Chicago Cubs, and interleague contests with the also-former rival Chicago White Sox.
- New York Mets v. New York Yankees (Subway Series)
- Oakland Athletics v. San Francisco Giants (Bay Bridge Series or Battle of the Bay)
- San Diego Padres v. Seattle Mariners
Split rivalries 
Beginning in 2013, the Boston Red Sox, Toronto Blue Jays, Atlanta Braves, and Philadelphia Phillies will form a "split rivalry." Odd years will feature Braves-Blue Jays and Phillies-Red Sox home-and-home series, while even years will feature Braves-Red Sox and Phillies-Blue Jays.
In the West, the Arizona Diamondbacks, Houston Astros, Texas Rangers, and Colorado Rockies will also have a split rivalry. Odd years will feature Rockies-Astros and Diamondbacks-Rangers home-and-home series, while even years will feature Rockies-Rangers and Diamondbacks-Astros.
Former interleague rivalries 
Ended in 2006, when the Washington Nationals replaced the Phillies as the Orioles' rival.
Ended in 2013, when the Astros moved to the American League West. The two teams now play each other 19 times a year as divisional rivals.
Ended in 2005, when the Expos moved to Washington DC.
Interleague play used to be scheduled in June and July (though as it was today if any teams were involved in interleague play, all teams were, except for the two NL teams that play each other). Later it was changed to occur only in June. In 2005, the format was changed again so that each team played one series during the third weekend in May and the rest of their games in mid-to-late June, occasionally stretching into early July, only playing interleague opponents until interleague schedule is complete for the year, allowing for more weekend interleague games than as opposed to playing all 18 games consecutively. In the American League, each team plays 18 games; in the National League, four teams played 18 games and twelve teams played 15 games. The reason for the difference was that during interleague play, all teams play interleague games at the same time, except for two NL teams that play each other. This was required because the NL had two more teams than the AL.
In 2013, for the first time in Major League Baseball's history, a game played on Opening Day was part of an interleague series. The game was between the Los Angeles Angels of Anaheim and the Cincinnati Reds, and was played on April 1, 2013.
As of 2012, every Major League team has had interleague series with each team in the opposing league. Some clubs have not hosted every team at their home ballpark.
- The Seattle Mariners have not hosted the Milwaukee Brewers since the Brewers' move into the National League in 1998. Over the same timespan, the Brewers have never hosted the Oakland Athletics.
- The Los Angeles Dodgers have never hosted the Tampa Bay Rays. This makes the Rays the only MLB team to have never visited Dodger Stadium.
- The Yankees have also not hosted the Dodgers in an interleague series, although they have played in Los Angeles twice since 2004. This makes the Dodgers the only current Major League franchise to have never played a regular season game in the original Yankee Stadium.
- The Kansas City Royals have never hosted the Atlanta Braves. This means that Chipper Jones, who played his entire MLB career with the Braves, did not get to play in Kauffman Stadium until the 2012 All-Star Game was held there in his final MLB season.
- The Toronto Blue Jays have never hosted the San Diego Padres.
- The Oakland Athletics have never hosted the Chicago Cubs.
- The Los Angeles Angels of Anaheim have never hosted the St. Louis Cardinals.
- The Cardinals have never hosted the Texas Rangers during the regular season, however, they hosted the Rangers during the 2011 World Series.
Of these matchups, San Diego-Toronto will be the last to occur; the other eight have been confirmed to occur with the release of the 2013 MLB schedule.
Effect of Astros joining AL on scheduling 
Starting in 2013, the Houston Astros will join the American League, giving each league 15 teams. This will force interleague play throughout the season. For the first time ever, teams will play interleague games even on opening day and during key division races all the way to the end of the season. This does not require expanding the number of interleague games, because the probability of an interleague game is 252/2430 or about 1 in 9.6 games (this number is not an integer because not all teams have the same number of interleague games). With an odd number of teams in each league, one team in each league would be the "odd man out" and have to play an interleague game to fill out the schedule, meaning as few as 1 in 15 games could be interleague (14 AL teams in 7 AL games, 14 NL teams in 7 NL games and 1 AL and 1 NL team in an interleague game). Despite this, there have been proposals to increase interleague play to 30 games. While the increase to 30 games is highly unlikely for the foreseeable future a smaller increase will take place immediately, having every team play 20 interleague games.
For the 2013 season, the 20 interleague games will be played in eight series. Each team will play one three-game series against four teams from one division in the other league, and two two-game series (one home, one away) against the remaining team in that division (this is, and has since 2002, been on a rotating basis. For 2013 the match-ups are AL East vs. NL West, AL Central vs. NL East, and AL West vs. NL Central, meaning the changes of the Astros and the small increase in interleague play will not affect the yearly rotation). The remaining four games will be played against a team's "natural rival" in two back-to-back two-game series. It is currently unclear how the schedule will work when a team's natural rival is a member of the division they are scheduled to play as part of the yearly rotation (this will first occur for all teams in 2015). For 2013, the natural rivalry games will be played from May 27–30. Teams will play in one city May 27 and 28, then travel to the other city for games on May 29 and 30. Because of the requirement of near daily interleague play (the only exception being if not all teams are playing) spreading out interleague play throughout the year, these dates will be the only time for the entire season that all teams will be in interleague play on the same day. There will, however, be times that slightly more than half of MLB will be in interleague play on the same day.
Most days, there will be either one or three interleague games as the average number of interleague games per day will be 1.68 [(20 interleague games per team x 30 teams in MLB)/(179 total days in baseball season (including off days and excluding the All-Star break)/2 teams per game], and with 15 teams in each league, the number of interleague games per day must be odd (as one and three are).
Division rotation 
|Seasons||NL East vs.||NL Central vs.||NL West vs.||AL East vs.||AL Central vs.||AL West vs.|
|1997, 1998, 1999, 2000, 2001, 2006, 2009, 2012||AL East||AL Central||AL West||NL East||NL Central||NL West|
|2002, 2004, 2007, 2010, 2013||AL Central||AL West||AL East||NL West||NL East||NL Central|
|2003, 2005, 2008, 2011||AL West||AL East||AL Central||NL Central||NL West||NL East|
Since its introduction, regular-season interleague play has continued to be a source of controversy among baseball fans and others both inside and outside the sport. Among the arguments used in favor of and in opposition to interleague play are the following:
- Interleague matchplay increases attendance, however these numbers may be skewed, as interleague games are primarily played on weekends, when attendance is higher across the board, and in June, when school is not in session and temperatures are higher than some of the other months of the season.
- Fans can see players they might not otherwise get to see, especially those who have only ever played in one league, such as Alex Rodriguez and Johnny Damon.
- Certain geographic rivalries are played out during the regular season that otherwise might not happen for years at a time. The Yankees now play 6 games against the Mets each season every year whereas they would only have gone head to head in the 2000 World Series if not for interleague play. From 1962 until interleague play, the Mets and the Yankees played each other in a single game, the annual Mayor's Trophy Game, which was an exhibition game even though it was played during the regular season.
- It creates matchups that might not have been seen in generations. For example:
- During the 2004 season, the Giants and Red Sox played each other for the first time since meeting in the 1912 World Series.
- The Red Sox had never played at Wrigley Field (an NL park since 1916) until 2005.
- In 2004, the Yankees and Dodgers met for the first time since the 1981 World Series at Dodger Stadium.
- In 2007, the San Francisco Giants hosted the New York Yankees for the first time in the regular season at AT&T Park in San Francisco.
- In 2008, the New York Yankees visited the Pittsburgh Pirates for the first time since the 1960 World Series.
- In 2011, the Chicago Cubs traveled to Fenway Park for a series with the Boston Red Sox in what was the Cubs' first visit to the stadium since the 1918 World Series.
- It allows for a rematch of the previous World Series. This has occurred in nine of the seventeen seasons of interleague play: 1997 (Atlanta Braves at New York Yankees), 1999 (New York Yankees at Atlanta Braves), 2000 (New York Mets vs. New York Yankees), 2001 (Arizona Diamondbacks at New York Yankees), 2004 (Boston Red Sox at St. Louis Cardinals), 2005 (Houston Astros at Chicago White Sox), 2006 (St. Louis Cardinals at Detroit Tigers), 2008 (Philadelphia Phillies at Tampa Bay Rays), and 2009 (Philadelphia Phillies at New York Yankees), but not since.
- It allows the relative strength of the two leagues to be measured against each other over 252 games per year (300 beginning in 2013), rather than just in the World Series once per year.
- There are many series that are not considered compelling; for example, series between currently poor-performing teams or teams with no historical or geographic connections, such as the "rivalry" series Padres vs. Mariners.
- American League pitchers generally do not like taking batting practice for the opportunity to bat in one or two games. These pitchers are also unaccustomed to running the bases, which can lead to injury and premature fatigue. (For example, Chien-Ming Wang suffered a season-ending lisfranc sprain on his right foot when running the bases during a Yankees-Astros game at Minute Maid Park on June 15, 2008.)
Most notably, teams no longer play identical opponents as their divisional rivals, and even where they do, they don't always play them an identical number of times. This can lead to "strength of schedule" disparities like those the NFL has to deal with on a yearly basis. For example, in any given season, one NL Central team might play every AL East team except the (strong) first place team, while another NL Central team plays all but the (weak) last place team. Another scheduling problem is that because the leagues are not equal in size, there always has to be one NL game on interleague days (interleague is done with block scheduling, so all the teams play interleague games on the same day, and all the interleague games are played in one part of the schedule (third weekend of May and much of June)). This will be remedied beginning with the 2013 Major League Baseball season, when the Houston Astros move from the NL Central to the AL West, giving all of the divisions in both leagues five teams each.
- The "rivalry" series that consist of six games a year for some teams leads to further scheduling inequities. For example, the New York Yankees play the recently poor New York Mets six times a year, while their division rival Baltimore Orioles must play the recently strong Washington Nationals six times a year. Starting in 2013, these rivalry series will be reduced to four games a year, two at each venue.
- The World Series and All-Star Game are robbed of the mystique that used to result from the two leagues playing completely exclusive schedules during the regular season: in the case of the World Series, the "best in the American League" playing the "best in the National League" for the only time that whole year.
- Some teams play a certain opposite-league team more than a certain same-league team. For example, the San Diego Padres played the Seattle Mariners (an American League team) six times during the 2012 season. However, the Padres only played the Washington Nationals (a National League team) 5 times in the 2012 season. Starting in 2013, no team will play any same-league opponent fewer than six times a year, while teams will play interleague opponents a maximum of four times per year.
- More games against interleague opponents means fewer games against same-league and division rivals – the latter of which may be more compelling. However, the leagues currently play an unbalanced schedule that favors divisional opponents rather than teams from other divisions (which is important due to the postseason qualifying structure - only the best team from a given division is guaranteed a berth in the postseason).
See also 
- Proposals for interleague play prior to 1997
- For head to head listings, choose team and the time period to get full list and results
- "Owners Back Inter-League Ball Series". Chicago Tribune. 1933-08-23.
- Drebinger, John (1956-12-06). "Player limit, Interleague Games Top Issues on Majors' Agenda". New York Times. Retrieved 2009-10-02.
- Hurwitz, Hy (1963-05-04). "Veeck Predicts Big Time Will Adopt Interloop Play". The Sporting News. p. 4.
- Koppett, Leonard (1976-02-18). "Drastic Changes Seen For Baseball". New York Times. Retrieved 2011-10-01.
- "Baseball Approves Interleague Play". New York Times. January 19, 1996. Retrieved 2011-10-01.
- "Who should sign Barry Bonds?". Hardballtimes.com. 2008-03-04. Retrieved 2013-02-28.
- "Red Sox’s David Ortiz ready to take the field in interleague play - MLB - Sporting News". Aol.sportingnews.com. 2012-05-18. Retrieved 2013-02-28.
- "Interleague History: All-Time Club Records in Interleague Play". MLB.com. Major League Baseball. 2010-06-28. Retrieved 2010-06-28.
- Interleague History (MLB.com/News/Awards/History/Interleague/Home). MLB Advanced Media, L.P. Retrieved 2009-08-31.
- Interleague History: Interleague Play Leaders (MLB.com/News/Awards/History/Interleague/All-Time Leaders). MLB Advanced Media, L.P. Retrieved 2009-08-31.
- "Reds use three homers to beat Angels". St. Louis Post Dispatch. April 5, 2013. Retrieved April 6, 2013.
- Kline, Jez (2010-06-15). "Behind Enemy Lines: Dodgers vs. Yankees". Scout.com. Retrieved 2010-06-17.
- "Increase in Interleague games unlikely in 2013 | MLB.com: News". Mlb.mlb.com. Retrieved 2013-02-28.
- "MLB's 2013 interleague schedule is a huge step in the right direction - ESPN". Espn.go.com. 2012-05-19. Retrieved 2013-02-28.
- The Enid News and Eagle, Enid, OK – Rivalies add to interleague play