The American and National Leagues are part of Major League Baseball (MLB), the highest level of professional baseball in North America. There are two main differences between the leagues: different teams play in each league, and the American League (AL) allows teams to use a designated hitter (DH). The use of the DH in the American League also results in more scoring and generally higher offensive statistics than in the National League (NL).
Numbers of Teams
Since 1960, the number of major league teams has risen from 16 to 30 as expansion teams have been added six times. The number of teams in each of the leagues has varied as teams have been added and has not always been equal. From 1998 to 2012, for example, there were 14 American League teams and 16 National League teams. In 2013, however, the Houston Astros were scheduled to move from the NL to the AL, giving each league 15 teams and making them equal sizes for the first time since 1997.
One reason why the leagues have often had unequal numbers of teams is because, for many years, AL and NL teams never played each other in non-exhibition games except during the World Series — the games that decide the major league championship. This meant that each league always needed an even number of teams, so that there would not be an idle team each day. In 1997, interleague games began being held during the regular season, which eliminated the need to have even numbers of teams in both leagues.
Composition of Leagues
The AL and NL each have teams throughout the United States and are divided into East, Central and West Divisions. The AL also has one team based in Canada, the Toronto Blue Jays. As teams have been added and have moved to different cities, the number and composition of the leagues' divisions have been adjusted. For metropolitan areas that have two teams, such as New York, Chicago and Los Angeles/Anaheim, the teams traditionally have been in opposite leagues.
The Designated Hitter Rule
In 1973, the American League added a rule that allows a team to use a designated hitter, a player who does not play defense in the field but instead takes the pitcher's spot in the batting order. This rule was adopted to add more offense to the game, because pitchers typically are among the teams' worst hitters — they are valued for their skills as pitchers, not hitters. As a result of the DH, American League teams, on average, score more runs per game, have higher batting averages and hit more home runs than NL teams, although that is not always true for individual teams.
The absence of a DH in the National League results in slightly different strategies being used in the NL. For example, NL managers often use pinch-hitters to bat for pitchers late in games. When this happens, the pitcher also must be replaced if and when that team goes back out to play defense. Many times, the pinch-hitter will remain in the game to play a defensive position, and the new pitcher will replace another player in the batting order; this is called a double switch. Another effect of not using designated hitters in the National League is that NL teams often keep more non-pitchers on their rosters than AL teams do, because NL teams sometimes must use multiple pinch-hitters to bat for pitchers in a game, rather than using only one DH.
During interleague games and the World Series, whether the DH is used depends on which team is the home team. When an American League team is the home team, the DH is used by both teams. If a National League team is the home team, then neither team can use a DH. There is some debate about whether AL or NL teams have an advantage in interleague play, with some people arguing that American League pitchers are at a disadvantage when they are forced to bat, because they are unaccustomed to it and rarely practice it. Other people say that AL teams have an advantage because they employ regular designated hitters who usually are among their teams' best hitters, and NL teams usually must use backup players as their designated hitters when the DH rule is in effect. Through the first 15 years of interleague play, AL teams won slightly more often — about 52 percent of the time.