Editing Baseball rules (section)

===Modern era (1901-present)===
Due to the frequent and often radical rule changes during this early period, the "modern era" is generally considered to have begun in 1901, when the [[American League]] was also formed.

Some significant rule changes continued in the first quarter of the 20th century, but were much less frequent. In 1903, the American League adopted the foul strike rule. In 1907, the sacrifice fly rule was adopted. In 1910, cork centers were added to balls. In 1925, the minimum distance for a home run was made 250 feet. Until 1929 (AL) and 1931 (NL), a ball that bounced over the outfield fence in fair territory was a home run, not a ground rule double.

After that, the rules remained virtually static for decades. Most top-level international leagues were formed during this period, including the [[Japanese Baseball League]] (1936) and its modern-day successor [[Nippon Professional Baseball]] (1950). Already-existing leagues in the Western Hemisphere were integrated into MLB's [[Minor League Baseball|minor leagues]] and thus subject to the OBR, namely the [[Cuban League]] (1947) and the [[Mexican League]] (1955).

In 1961, the 162-game schedule was adopted by MLB. In 1969, the pitcher's mound dropped five inches and the strike zone was reduced from the armpits to the top of the knees. In 1973, the American League adopted the [[designated hitter]] rule. This was probably the most controversial rule change in baseball's history and is still subject to lively debate. It was not adopted by the National League until 2022. Also controversial when adopted was the later introduction of [[interleague play]]. On the other hand, rule changes banning the use of steroids and other performance-enhancing substances have had widespread support as protecting the integrity of the game. 

The most recent significant rule changes to the OBR occurred in 2023, when [[Commissioner of Baseball|MLB Commissioner]] [[Rob Manfred]] introduced rules adding a [[pitch clock]], extra-inning base runners, and restricting [[infield shift]]s. These rules have been gradually adopted in North America (and in WBSC competition), but generally do not exist elsewhere in the world.