Interleague play in Major League Baseball refers to regular-season baseball games played between an American League (AL) team and a National League (NL) team. Interleague play was first introduced during the 1997 Major League Baseball season. Prior to that, matchups between AL teams and NL teams occurred only 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.
Regular season interleague play was discussed for baseball's major leagues as early as 1903, when the two major leagues made peace and formed the National Commission as governing body. The first National Commission Chairman, Cincinnati president August Herrmann (who had already been a proponent of interleague play), proposed an ambitious scheme in late 1904. Herrmann's plan would have seen the two leagues ending their seasons earlier, after approximately 116 games, "and then have every National League team play two games in every American League city, and have every American League team play two games in every National League city." Another interleague play idea was floated around the same time by Boston Americans owner John Taylor, whose plan was for each league to play its full 154-game schedule, to be followed by not just a championship series between the two league winners, but also by series between the two second-place finishers, the two third-place teams, and all other corresponding finishers.
In August 1933, several owners reacted favorably to a proposal by Chicago Cubs president William Veeck to have teams play four interleague games in the middle of the season, beginning in 1934. 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 formally approved until 1996, at least in part as an effort to renew the public's interest in MLB following the 1994 players' strike.
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's 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 Darryl Hamilton got the first base hit in interleague play, while Stan Javier hit the first home run, leading the Giants to a 4–3 victory over the Rangers.
From 1997 to 2001, teams played against the same division from the other league; for example, the American League West played teams from the National League West, typically scheduled to alternate between home and away in consecutive years. In 2002, however, 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. 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 (with the exception of games postponed by weather that were made up after the All-Star Game). Most games were played in June and early July, although beginning in 2005, interleague games were played during one weekend in mid-May.
The designated hitter (DH) rule was originally 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 had the option to use a DH, while in a National League ballpark, both teams' pitchers were required to bat. 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 spent his entire career in the American League and was the Red Sox's regular DH, was assigned to play first base when the Red Sox had away interleague games, with the Sox choosing to give up good fielding in favor of retaining Ortiz's power hitting. With the introduction of the DH to the National League in 2022, this no longer applies.
In 2007, two teams – the Los Angeles Dodgers and the Baltimore Orioles – played six games with more than one interleague opponent. The Dodgers played both the Toronto Blue Jays and the Los Angeles Angels while the Orioles 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 six games. The Miami Marlins also did this, playing both the Tampa Bay Rays and Boston Red Sox for six games each.
The first Civil Rights Game was an exhibition interleague game between the Cleveland Indians and St. Louis Cardinals at AutoZone Park in Memphis on March 31, 2007. The first regular season Civil Rights Game was an interleague game between the Chicago White Sox and Cincinnati Reds at Great American Ball Park on June 20, 2009.
Since the introduction of interleague play, two teams have shifted leagues: the Milwaukee Brewers from the American League to the National League in 1998, and the Houston Astros from the National League to the American League in 2013. As a result, a 2013 interleague series between the two teams made it the first time that two teams faced each other in an interleague series after both teams previously faced each other in an interleague series representing opposite leagues: the two teams met from September 1–3, 1997 (Houston in NL, Milwaukee in AL), then again from June 18–20, 2013 (Houston in AL, Milwaukee in NL). In both instances, the series took place in Houston, with the team representing the American League winning 2–1. From 1998 to 2012, both teams were division opponents in the National League Central.
For the 2020 season, all interleague games featured the DH, as the National League used the rule for the first time in its history due to health and safety measures related to the COVID-19 pandemic. The DH became permanent in the NL for the 2022 season.
Interleague play has largely favored the American League in terms of win–loss records. In 25 years of play, the AL has won the season series 18 times, including 14 straight from 2004 to 2017. The National League has won 6 and one season ended in a tie. With the Pirates beating the Royals on September 19, 2018, the National League guaranteed a season series win for the first time since 2003.
As of the end of the 2018 MLB season, the American League holds an all-time series advantage of 3,032–2,732 and has finished with the better record in interleague play for 14 straight seasons, dating back to 2004 until 2018. 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).
|Year||Best record||Total games||American League||National League||Winning pct.*||Notes|
The following is the 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."
See also: Major League Baseball rivalries
Certain interleague matchups are highly anticipated each year, due to the geographic proximity of the teams involved. Many cities, metropolitan areas and states contain at least one team in each league. In each of these "natural rivalry" matchups, the two teams meet annually for four games, two in each ballpark. Before 2013, and 2015, 2018, 2020, and 2021, there were six games between the two teams, three per ballpark:
In 2014, the ten teams that qualified for the postseason were five pairs of geographical rivals: the Angels, Athletics, Orioles, Royals, and Tigers from the AL; and Dodgers, Giants, Nationals, Cardinals, and Pirates from the NL.
Four teams in the East and West formed a "split rivalry" where the rivalry pairings alternated in odd- and even-numbered years.
In the East:
In the West:
In years in which the AL East plays the NL East and the AL West plays the NL West (2015, 2018, etc.), the teams play their assigned "rival" for the year six times and the other "rival" either three or four times.
From 2023 onwards, the interleague schedule was modified, with four games played between rivals, ending the use of split rivalries.
1997 was the first year of regular season interleague play. The 20 teams in the East and Central divisions played 15 games each in five three-game series. The eight teams in the West divisions played 16 games each in eight two-game series, playing home and away two-game series against each team.
1998 had the MLB add the Devil Rays and Diamondbacks as expansion teams. All the teams in the American League played 16 games, playing one four-game series (split into two home, two away) and four three-game series and the National League played games from a range between 12 and 16 games, depending on the team. Despite their move from the American League to the National League, the Milwaukee Brewers still did not play all of the Major League teams until 2005 when they played the then Tampa Bay Devil Rays in an interleague series, because the Brewers left the AL the same year the Devil Rays joined it
From 1999 through 2012, each team in the American League played 18 interleague games a year, but because the National League had two more teams than the American, only four NL teams would play a full 18-game interleague schedule, with the remaining twelve teams playing only 15. With the exception of the two NL teams playing each other, all teams were involved in interleague play at the same time (originally in June and July), playing only interleague opponents until the interleague schedule was complete for the year. The schedule was later changed to occur only in June; in 2005, it was changed again to allow for more weekend interleague games, with each team playing one series during the third weekend in May and the rest in mid-to-late June (occasionally stretching into early July).
In 2013, the Houston Astros joined the American League, giving each league 15 teams and thereby necessitating that interleague games be played throughout the season, including on Opening Day and during key division races all the way to the end of the season. This did not require expanding the total number of interleague games, because the probability of an interleague game during the era in which the Astros played in the NL was 252/2430 or about 1 in 9.6 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 or beyond. A smaller increase took place immediately, having every team play 20 interleague games starting 2013.
From 2013 to 2022, each team played 20 interleague games across eight series. Each team played 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. Divisions had been rotated since 2002 but teams did not necessarily play everyone in that division prior to 2013. The remaining four games were played against a team's "natural rival" in home and home two-game series. From 2013 to 2017 these two series were back-to-back at one venue on Monday and Tuesday and at the other team's venue that Wednesday and Thursday. Should a team's natural rival be a member of the division they are scheduled to play as part of the yearly rotation (this first occurred for all teams in 2015), the team would play home-and-home three game series against the natural rival, home-and-home two game series against two other opponents, and single three game series against the last two (one home, one away). Because the requirement for nearly daily interleague play (the only exception being if not all teams are playing) spreads out interleague play throughout the year, not every team will be in interleague play on the same day. Due to the 2016 CBA lengthening the schedule by four days, 2018 was the first year during which no team was required to play back-to-back home-and-home two game series against any other team.
In 2020 due to the COVID-19 pandemic the schedule was shortened from 162 games to 60 and interleague opponents were switched to the corresponding divisions. The teams played 20 interleague games using the same format that was in place in 2015 and 2018, when the same geographic divisions were aligned together for interleague play. The originally scheduled rotation of AL Central vs NL West, AL East vs NL Central, AL West vs NL East was moved to 2022.
As part of the 2022 CBA, interleague play was expanded from 20 to 46 games per team per season, starting in 2023.  Each team will play a four game home-and-home series against its natural rival and a single three game series against the other 14 interleague opponents, with the venue alternating every other year.
Most days, there will be either one, three, or five interleague games as the average number of interleague games per day will be 3.77 [(46 interleague games per team x 30 teams in MLB)/(183 total days in baseball season, including off days, but excluding the All-Star break)/2 teams per game]. With 15 teams in each league, the number of interleague games is almost always odd, with exceptions based on when teams from each of the AL and NL have the same off day. Doubleheaders and make-up games also apply should a rainout or other extended delay requires one or more games to be postponed.
On April 1, 2013, for the first time in major league baseball history, an interleague game was played on Opening Day, between the Los Angeles Angels of Anaheim and the Cincinnati Reds at Great American Ball Park, with the Angels claiming the distinction of winning that game, 3–1, in 13 innings. Also, on September 29, 2013, for the first time in major league baseball history, an interleague game was played on the last day of the regular season, between the Miami Marlins and the Detroit Tigers at Marlins Park. The Marlins not only claimed the distinction of winning that game, 1–0, in walk-off fashion, but also saw their pitcher Henderson Álvarez pitch a no-hitter, marking just the 7th time a no-hitter was tossed in an interleague contest.
On April 3, 2016, for the first time in MLB history, the previous year's World Series participants faced off on Opening Day the following year. The Kansas City Royals hosted the New York Mets at Kauffman Stadium in a nationally televised game and won, 4–3.
With the Pittsburgh Pirates' victory over the Oakland Athletics on July 10, 2013, every team has beaten every other team at least once; the A's had previously been 11–0 all time against the Pirates.
Every team has also hosted and visited every other team at least once. This distinction was completed in July 2016 when the San Diego Padres made their first trip to Toronto. The two teams had previously played in San Diego in 2004, 2010, and 2013.
In 2020, for the first time ever, both leagues split the games that they played between each other, with each team winning 149.
During 1997–2001, the divisions were paired with their geographical counterpart (AL East vs. NL East, AL Central vs. NL Central, AL West vs. NL West). Beginning in 2002, the divisional pairings rotated. The geographical counterparts were initially skipped in 2004, but returned to the schedule in 2006, creating a three-year rotation that remains in use. In 2020, due to the COVID-19 pandemic, the originally scheduled matchups were adjusted in order to limit travel. Divisional pairings before 2023 were:
|Season||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, 2015, 2018, 2020, 2021||AL East||AL Central||AL West||NL East||NL Central||NL West|
|2002, 2004, 2007, 2010, 2013, 2016, 2019||AL Central||AL West||AL East||NL West||NL East||NL Central|
|2003, 2005, 2008, 2011, 2014, 2017, 2022||AL West||AL East||AL Central||NL Central||NL West||NL East|
Starting in 2023 with the new collective bargaining agreement, every team will play every other team regardless of league, for a total of 46 games per season. The format is a four game home and home series against the geographic rival and a single three game series against the other 14 interleague opponents, with location to rotate every other year.
Since its introduction, regular-season interleague play has continued to be a source of controversy among baseball fans and others involved with the sport. Among the arguments used in favor of and in opposition to interleague play are the following: