With the Houston Astros moving to the American League starting in 2013, each league (National and American) will have an even amount of teams (15). As a result, the debate regarding designated hitters (DH) is heating up. As it currently stands, the AL uses designated hitters while the NL does not.
Why are designated hitters used in the AL, but not in the NL? Are there any specific reasons why the AL adopted the rule and/or the NL did not?
One would think that this rule would be used MLB-wide to keep things consistent...rather than having to play by the respective rules of the home team's league during interleague play, when a player gets traded from one team in one league to another team in the other league, etc. However, the MLB claims that the DH has become "a role more than a player."
Pitchers have historcally had low batting averages. In 1973, American League owners voted 8-4 in favor of using a designated hitter to replace a pitcher's at-bat. Since, the AL has generally had a higher batting average than the NL. The DH was first used in the World Series in 1976 and for even-numbered years until 1985, where the DH would only be used when games were held at an AL team's stadium (when interleague play (NL vs. AL) began in 1997, the DH would be used in the same fashion). These days, the DH position is used for players to rest and take a partial day-off rather than a full-time position. Also, the DH position has diminished the use of the double switch in the AL, but is still rather prevalent in the NL.