The Pitcher's Mound
Sixty feet six inches away and ten inches up, and both numbers have been changed to fix the game before.
What it actually is. The mound is a raised circle of dirt eighteen feet across with a rubber slab set into it, twenty four inches by six. The front edge of the rubber is sixty feet six inches from the back point of home plate and the mound is ten inches higher than the field. A pitcher must have contact with the rubber when he delivers.
What somebody who knows the game gets out of it. The height of the mound is a lever the sport has pulled to change scoring, which is worth knowing because it means the run environment is a policy decision rather than a natural constant. After the 1968 season, when the league hit .237 and the ERA was 2.98, the mound was cut from fifteen inches to ten and the strike zone shrunk, and offense returned immediately. The other number that matters is one nobody legislated: extension, how far down the mound a pitcher releases the ball, which effectively shortens the distance and makes 95 play like 97.
The numbers worth knowing. Sixty feet six inches, ten inches high, an eighteen foot circle. Average extension is around six and a half feet, so the ball is actually released around fifty four feet from the plate. A pitch at 95 mph crosses that in under four tenths of a second.
What people get wrong about it. The distance is measured to the back point of home plate, not to the front, and the sixty feet six inches is famously the product of a surveying quirk rather than design. The mound is also the only raised area on a level playing field in any major sport, which is why pitchers talk about the feel of a specific mound as a real thing rather than a superstition.
At Little League and travel ball. Distances scale with age: 46 feet at Little League Majors, 50 to 54 in the middle travel ages, and 60 feet 6 inches from about 14U. Many youth fields have flat mounds or portable ones. The jump from 46 to 50 feet and again to 54 is where most young pitchers' command temporarily falls apart, and it is normal rather than a mechanical problem.
Batter's Eye: look up anything in baseball