Question: What is the rule that makes a major difference between the National League and the American League that allows another player to bat for the pitcher?

Passages:
The History of the American League, officially known as the American League of Professional Baseball Clubs and often abbreviated AL, stretched back into the late-19th century.  Prior to 2000, when the AL and NL were dissolved as separate entities and merged into the organization called Major League Baseball, the American League was one of the two leagues that made up major league baseball.  Originally a minor league known as the Western League, the league later developed into a major league after the American Association disbanded.  In its early history, the Western League struggled until 1894, when Ban Johnson became the president of the league.  Johnson led the Western League into major league status and soon became the president of the newly renamed American League.  The American League has one notable difference over the National League, and that is the designated hitter rule.  Under the rule, a team may use a batter in their lineup who is not in the field defensively, compared to the old rule that made it mandatory for the pitcher to hit. In baseball, the designated hitter rule is the common name for Major League Baseball Rule 5.11, adopted by the American League in 1973.  The rule allows teams to have one player, known as the designated hitter (abbreviated DH), to bat in place of the pitcher.  Since 1973, most collegiate, amateur, and professional leagues have adopted the rule or some variant.  MLB's National League and Nippon Professional Baseball's Central League are the most prominent professional leagues that do not use a designated hitter. The Chicago White Sox are a Major League Baseball franchise based in Chicago.  They play in the American League Central division.  Pitchers for the White Sox have thrown eighteen no-hitters in franchise history.  A no-hitter is officially recognized by Major League Baseball only “when a pitcher (or pitchers) allows no hits during the entire course of a game, which consists of at least nine innings.  In a no-hit game, a batter may reach base via a walk, an error, a hit by pitch, a passed ball or wild pitch on strike three, or catcher’s interference.”  No-hitters of less than nine complete innings were previously recognized by the league as official; however, several rule alterations in 1991 changed the rule to its current form.  A no-hitter is rare enough that one team in Major League Baseball has never had a pitcher accomplish the feat.  Three perfect games, a special subcategory of no-hitter, have been pitched in White Sox history, which equals the New York Yankees for the most perfect games pitched by any MLB franchise.  As defined by Major League Baseball, “in a perfect game, no batter reaches any base during the course of the game.”  These feats were achieved by Charlie Robertson in 1922, which was the first perfect game on the road in MLB history, Mark Buehrle in 2009, and Philip Humber in 2012. Jeared Wells "Bill" Pounds (March 11, 1878 – July 7, 1936) was a pitcher in Major League Baseball.  He appeared in just two major league games, one each for Cleveland and Brooklyn in 1903, but the only surviving images of him in a major league uniform show him with the New York Highlanders.  Bill Pounds was born in Paterson, New Jersey, and had a long career as a minor league pitcher.  His professional career began in 1899 when he pitched for both Binghamton and Paterson.  After a year out of organized baseball, he played in 1901 and 1902 for two Ilion and Utica in the New York State League.  After reportedly signing a contract to return to Utica for 1903, he was signed by Cleveland in the American League and was on their Opening Day roster.  Pounds was brought in to pitch on May 2 in the fourth inning in Chicago when the White Stockings had opened up a big lead; he gave up seven runs (six earned) on eight hits in the 16-6 loss.  On May 18 he was released by Cleveland and was signed shortly thereafter by the New York Highlanders.  Pounds was in uniform with the team when the Highlanders visited Chicago for a series May 20–22.  A photographer from the Chicago Daily News was taking pictures of the players on the teams visiting both the American League and National League ballparks, and during this visit Pounds had his image preserved for posterity.  Before the end of the month, without having appeared in a game for New York, Pounds was sent back to Cleveland, apparently because he could not come to terms on a contract.  On June 4 he was signed by Brooklyn of the National League, but he did not appear in a game until June 30.  With Pittsburg ahead 12-0 after three innings, Pounds was sent in to pitch.  He allowed five runs (four earned) in six innings on eight hits and two walks in the 17-8 loss, and gave up a long home run to Honus Wagner.  On July 3, his contract was transferred to Baltimore of the Eastern League, along with that of Hughie Jennings and three other Dodgers.  Pounds would never appear in another major league game; though his pitching record was unimpressive, he finished with a lifetime batting record of three hits in five at-bats.  Late in the 1903 season, his contract was purchased by Denver, but it is unclear whether he actually played in Colorado.  For the remainder of his minor-league career, from 1904 through 1911, he pitched for teams within a couple of hundred miles of his birth—four teams in the New York State League and two in the Tri-State League.  In the off-seasons he would sometimes pitch for the Paterson Elks team, and he continued to pitch for them after his minor-league career had ended.  According to The Sporting Life, “Pounds has speed and a rather good assortment of curves.  He has not the best control in the world.”  A few years after his career had ended, the Utica Observer described him in this way: “Bill Pounds was the champion sweater of the league.  He perspired so much that…a miniature lake (formed) around the slab.”  He died in 1936 in the city of his birth, aged 58.  Early in the 21st century, the photographic archives of the Chicago Daily News were posted online.  Although his teammates’ photographs were easily identified, the image of Pounds remained unidentified, or occasionally misidentified as Doc Adkins, for at least a decade. The paixiao (traditional: 排簫; simplified: 排箫; pinyin: "páixiāo"; also pái xiāo, pai-hsiao, pronounced ] ) is an ancient Chinese wind instrument, a form of Pan flute.  A major difference between the Chinese Paixiao and the panpipes used in European and South American traditions, is that at the top of the Chinese instrument the pipe holes are each cut angled or with notches.  This allows for bending the pitch in similar capacity to the dongxiao down a minor second.  This allows Chinese paixiao to be fully chromatic without loss in timbre, even though the included pipes are tuned diatonically. A defensive substitution in the game of baseball occurs when a currently non-playing player is placed into the field in place of another player, typically due either to injury or the appearance of a pinch hitter.  In the American League, a pinch hitter is usually substituted for the position player in whose place he batted (although another common substitution is pinch-hitting a utility infielder for a second baseman and subsequently switching him for the shortstop in the field while moving the shortstop over to the now-vacant second base position).  In the National League, which does not use the designated hitter rule, pinch hitters sometimes bat for pitchers. However, another common pitcher-substitution strategy in the NL is the double switch, in which a pitching change is coupled with a pinch-hitter who is also defensively substituted for a second player. The Houston Astros (formerly known as the "Houston Colt .45s" from 1962–64) are a Major League Baseball franchise based in Houston, Texas.  Formed in 1962, they play in the American League West division (formerly in the National League Central division until 2012).  Pitchers for the Astros have thrown eleven no-hitters in franchise history.  A no-hitter is officially recognized by Major League Baseball only “when a pitcher (or pitchers) retires each batter on the opposing team during the entire course of a game, which consists of at least nine innings”.  No-hitters of less than nine complete innings were previously recognized by the league as official; however, several rule alterations in 1991 changed the rule to its current form.  A no-hitter is rare enough that one team in Major League Baseball has never had a pitcher accomplish the feat.  No perfect games, a special subcategory of no-hitter, have been thrown in Astros history.  As defined by Major League Baseball, “in a perfect game, no batter reaches any base during the course of the game.” In baseball, batting average (AVG) is a measure of a batter's success rate in achieving a hit during an at bat.  In Major League Baseball (MLB), it is calculated by dividing a player's hits by his at bats (AB).  In MLB, a player in each league wins the "batting title" each season for having the highest batting average that year.  The American League (AL) winner is known as the "Rod Carew American League Batting Champion", while the National League (NL) leader is designated the "Tony Gwynn National League Batting Champion".  Under current rules, a player must have 3.1 plate appearances (PA) per team game (for a total of 502 over the current 162-game season) to qualify for the batting title.  However, if a player's lead in AVG is sufficiently large that enough hitless at bats can be added to reach this requirement and the player still would have the highest batting average, he wins the title.  Tony Gwynn, for example, had 159 hits in 451 ABs in 1996 (.353 average) but only 498 PAs.  Gwynn's batting average would have dropped to .349 (159 hits in 455 ABs) with four hitless ABs added to reach the 502 PA requirement, but this would still have been higher than the next-highest eligible player (.344 average), so he was awarded the 1996 NL batting title. The Milwaukee Brewers (formerly known as the "Seattle Pilots" in 1969) are a Major League Baseball franchise based in Milwaukee, Wisconsin.  Formed in 1969, they play in the National League Central division (formerly in the American League Central Division until 1997).  Juan Nieves threw the only no-hitter in franchise history on April 15, 1987.  A no-hitter is officially recognized by Major League Baseball only "when a pitcher (or pitchers) retires each batter on the opposing team during the entire course of a game, which consists of at least nine innings".  No-hitters of less than nine complete innings were previously recognized by the league as official; however, several rule alterations in 1991 changed the rule to its current form.  A no-hitter is rare enough that a Major League Baseball team, the San Diego Padres, has never had a pitcher accomplish the feat.  A perfect game, a special subcategory of no-hitter, has yet to be thrown in Brewers history.  As defined by Major League Baseball, "in a perfect game, no batter reaches any base during the course of the game." The 1986 Major League Baseball All-Star Game was the 57th playing of the midsummer classic between the all-stars of the American League (AL) and National League (NL), the two leagues comprising Major League Baseball.  The game was held on July 15, 1986, at the Astrodome in Houston, Texas, the home of the Houston Astros of the National League.  The game resulted in the American League defeating the National League 3-2 and ended a streak where the NL won 13 of the last 14 games.  Boston Red Sox pitcher Roger Clemens was named the Most Valuable Player.

Supporting sentences:
 The American League has one notable difference over the National League, and that is the designated hitter rule. In baseball, the designated hitter rule is the common name for Major League Baseball Rule 5.11, adopted by the American League in 1973.  The rule allows teams to have one player, known as the designated hitter (abbreviated DH), to bat in place of the pitcher.