The designated hitter rule allows teams to substitute the pitcher in their batting order with another player, known as the designated hitter or DH.
The DH does not play a fielding position when his team is not batting. By substituting the pitcher with the DH, the pitcher does not bat.
The DH rule is used throughout most levels of the Bull Baseball League with the exception of the high-school level Nor-Am High School League, and the Can-Am College League, both of which removed it after the 2017 season.
The DH Rule
As the DH does not play a fielding position, and only bats, there are special rules which apply to the DH position. Generally, any substitution that results in the DH changing positions in the batting order, or that results in a pitcher batting or the DH taking a fielding position, will void the DH position for that game, and the pitcher must then bat in the order.
The DH rule is an optional rule, meaning that at the beginning of a game, either team may elect to have their pitcher take a place in the batting order, and dispense with using a DH for the game.
Historically, pitchers were used for their specialized skills in pitching, and not necessarily for hitting. The DH rule came about in baseball as a way of protecting pitchers from having to bat and risk injuries from batting or base running. In addition, pitchers typically spend a great deal of time perfecting their craft, leaving little time to develop hitting.