The baseball rule is 6.10 and it was passed in January of 1973 and the Boston Red Sox quicky struck first. The rule has had profound changes on the dynamics of baseball and has resulted in a continuing war of words since its implementation – the designated hitter (DH) rule.
The rule historically goes back to the Deadball Era and was proposed by Connie Mack, among others. Mack was in a funk over watching members of his staff flail away attempting to hit. The rule also gathered some traction from an unusual source in the 1920s – National League President John Heydler, who wished to speed up the game.