From BR Bullpen
The Designated Hitter, commonly referred to as DH, is a player in the batting order to hit only but not play defense. He hits in place of the pitcher. If the DH is replaced by a player who then takes a position, the pitcher must bat in the designated hitter's place. The Designated Hitter is often considered the most significant rule change to occur in baseball's modern era.
 Use in Major League Baseball
The Designated Hitter is used only in the American League (since 1973) and was never adopted in the National League. The rule allowing a DH has always been controversial since some want the rule eliminated, some want the rule adopted in both leagues and some want the rule to remain in its current state. NL teams use a DH in road games during interleague play, while AL teams have the pitcher bat in road games in interleague match-ups.
While critics of the DH suggest that it was designed to allow poor fielders to remain in the game despite their defensive flaws, it has not always been used that way. Many Designated Hitters have been players who were capable fielders who were injury-prone and kept from fielding to preserve their health. Paul Molitor, the first Hall of Famer to play more games as DH than any other position, fell into this category. Some teams don't even have a regular DH and instead use it to give their regular position players a break from fielding.
Ron Blomberg of the New York Yankees was the first player to bat as a designated hitter. Hal McRae was the first player to spend most of his career as a DH; other all-time leaders at the position include Edgar Martinez, Harold Baines and David Ortiz, who is now the career leader for hits, home runs and RBIs at the position.
 Use in Minor League Baseball
The DH was first used in the American Association in 1969. Usage in the minors changed over time - originally, individual organizations had some say in whether their teams used the DH or not. For a while, the Cincinnati Reds were adamant about having their pitchers bat for all their minor league affiliates. At other points a team would have their pitcher bat while their opponent used a DH. Since the late 1980s, usage has become the following: in AA and AAA games, the DH is used unless both teams are farm clubs of NL teams, in which case pitchers bat. In class A or lower games, the DH is always used.
Though it is officially a AAA league, the Mexican League uses a DH in all games.
 Use in Japanese Baseball
In Japan, the Pacific League adopted the DH in 1975. In 1988, the minor league Eastern League and Western League used it, but Central League farm clubs are allowed to opt out. The Central League never used the DH until interleague play began in 2005, when they used a DH on the road against Pacific League teams. In 2014, Japan flipped the rules for interleague games, using DH on the road at Central League parks but not at PL parks.
 The DH Rule
There are a few peculiarities to the DH Rule (rule 6.10 of the Major League Baseball Rules):
- The DH is optional. A team may decide to bat its pitcher and not use a designated hitter in a game where it would normally be used. A few instances were Ferguson Jenkins on October 2, 1974 for the Texas Rangers against the Minnesota Twins; Ken Holtzman on September 27, 1975 for the Oakland A's against the California Angels; Ken Brett for the Chicago White Sox on July 6, 1976 at the Boston Red Sox; and Brett again on September 23, 1976 for Chicago against the Twins. Rick Rhoden, a pitcher, was a DH on June 11, 1988 for the Yankees against the Baltimore Orioles in a game in which he was not pitching.
- The DH can play in the field, but once a manager decides to play him on defense, the pitcher immediately takes over the batting spot of the defensive player which the DH replaced (unless there are multiple substitutions, in which case the manager can decide where the pitcher will bat). The team then forfeits the use of the DH for the rest of the game. This happens a few times every season, and sometimes results in a pitcher being forced to bat in an AL game.
- The DH spot is locked in the order. If the DH bats, for example, fifth in the order, no substitution can be made to move him to fourth or sixth, or anywhere else.
- Any substitute for the DH, including pinch hitters and pinch runners are automatically considered to be the new DH, and the restrictions outlined above apply to them as well. These substitutes are listed in the boxscore as "Smith ph-dh" or "Smith pr-dh". This is how a number of AL pitchers end up with games as DH in their statistics: these are almost always the result of being used as a pinch-runner for the DH.
 The Phantom DH
The DH listed in the starting line-up must bat at least once before being substituted, unless there is an injury or the opposite team's starting pitcher has been changed. This rule was added after the 1980 season to close a loophole discovered by Orioles manager Earl Weaver: he would list one of his inactive starting pitchers in the starting line-up as a phantom DH, and then, when his first time to bat came up, Weaver could decide which of a number of players to use as a pinch hitter for his DH, depending on the situation (for example if there were men on base, if he needed a baserunner, etc). Pitchers Steve Stone and Dennis Martinez were used most often in this capacity. Boxscores from that time would list the pitchers as having played a game at DH, but after the amendment to the rule was adopted, these "appearances" were erased from these pitchers' records.
 Other versions of the rule
- Rule A allowed for a pinch-hitter to bat for the pitcher twice in a game with the pitcher remaining in the game. The pitcher could be used to bat for himself at anytime. An example is a pinch-hitter batting for the pitcher the first time and fourth time; the pitcher could bat the second at bat; another pinch-hitter could bat the third time. A pinch-hitter could play defensively, if he took the field the next half-inning after batting. The pitcher would bat in the replaced player's spot.
- Rule B was the DH rule that would eventually be the standard in the American League, except that the player could not go in defensively later.
- Rule C allowed for a pinch-runner only twice in a game for the pitcher or pinch-hitter in Rule A or DPH in Rule B. The pinch runner could enter defensively at any time, even though he appeared twice as a runner.
 Further Reading
- AJ Cassavell: "Universal truth? Execs talk NL DH possibility", mlb.com, January 16, 2016. 
- John Cronin: "The DH in the World Series: Interesting Facts", The Baseball Research Journal, SABR, Volume 40, Number 2 (Fall 2011), pp. 53-54.
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