when did the designated hitter come in play
In Major League Baseball, the designated hitter is a hitter who does not play a position, but instead fills in the batting order for the pitcher. The DH may only be used for the pitcher (and not any other position player), as stated in Rule 6.10. Use of the DH is optional, but must be determined prior to the start of the game. If a team does not begin a game with a DH, the pitcher (or a pinch-hitter) must bat for the entire game.