On January 11, 1973, the owners of America’s 24 major league baseball teams vote to allow teams in the American League (AL) to use a “designated pinch-hitter” that could bat for the pitcher, while still allowing the pitcher to stay in the game.

The idea of adding a 10th man to the baseball lineup to bat for the pitcher had been suggested as early as 1906 by the revered player and manager Connie Mack. In 1928, John Heydler, then-president of the National League (NL), revived the issue, but the rule was rejected at that point by the AL management. By the early 1970s, Charlie Finley, the colorful owner of the Oakland A’s, had become the designated hitter rule’s most outspoken advocate, arguing that a pinch-hitter to replace the pitcher–a player that usually batted poorly, exceptions like the legendary Babe Ruth notwithstanding–would add the extra offensive punch that baseball needed to draw more fans.

At a joint meeting of the two major leagues in Chicago on January 11, 1973, presided over by baseball commissioner Bowie Kuhn, the owners voted to allow the AL (which lagged behind the NL in both scoring and attendance) to put the designated hitter rule into practice. The NL resisted the change, and for the first time in history, the two leagues would play using different rules. Though it initially began as a three-year experiment, it would be permanently adopted by the AL and later by most amateur and minor league teams.

On April 6, 1973—Opening Day—Ron Blomberg of the New York Yankees became the league’s first ever designated hitter. In his first plate appearance, he was walked on a full count by the Boston Red Sox pitcher Luis Tiant. From the beginning, baseball purists decried the designated hitter in bitter, moralistic terms, arguing that it took away from baseball’s integrity. The rift between pro- and anti-designated hitter fans has continued into the present day. At first, the designated hitter rule did not apply to any games in the World Series, in which the AL and NL winners met for the world championship. From 1976-1985, it applied only to Series held in even-numbered years, and in 1986 the current rule took effect, according to which the designated hitter rule is used or not used according to the practice of the home team.