A regulation pitcher's mound is 18' in diameter, the center of which is 59' from the back of home plate. The pitcher's plate (or pitching rubber as it is commonly called) is 18" behind dead center of the mound. The slope from the rubber shall begin 6" in front of the rubber and will slope toward home plate 1" for every 1'. The rubber rests 6" inside the front edge of a level area 5' wide and 34" deep and shall not be more than 10" higher than the playing field.
This was not always true. During different periods in baseball history, the mound has been much taller. The mound in Philadelphia's Shibe park was rumored to be 20" high at one time, and the mound throughout baseball in the late 60s was as high as 16". It wasn't until 1969 that it was lowered to today's standard.
The original rules stipulated that the pitching rubber be 45 feet from the plate. It has been moved back twice, first to 50 feet, then to it's present day measure in 1893, presumably to give batters a better chance to hit and/or get out of the way of errant pitches. Daniel Adams, the first chairman of the Committee on Rules and Regulations, was the man who claimed to have set the original 45 foot distance. It has been said that the precise distance it stands today was the result of a measuring error (it was supposed to be 60') and that they simply decided to leave it.
Additional history of the pitching mound comes from statistician Bill Deane, who informs, "The first mention of the mound in the official baseball rules appears in 1903. Installed "to prevent trickery," Rule 1, Section 2 required that "the pitcher's plate shall not be more than 15 inches higher than the base lines or home plate." The height was reduced to ten inches in 1969.
Obviously, mounds were in use before they were standardized. Speculation is that they evolved as a matter of grounds keeping practice, for better drainage and water absorption. After overhand pitching was legislated in 1884, pitchers undoubtedly found the mounds to be an advantage: the downward weight-shift and momentum enable them to generate greater velocity on their pitches. John Montgomery Ward, who pitched in the major leagues 1878-84, supposedly took credit in later years.
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