Why Is a Baseball Field in the Shape of a Diamond?

The specifics of a baseball field have been hallowed by time and consecrated by tradition. The field has a unique mixture of regulation distances and individual variables that help lend the game its sense of charm. But non-fans--and even a few enthusiasts here and there--may wonder why someone chose to make baseball fields in the shape of a diamond. It actually stems from some very practical considerations regarding game play.

A baseball diamond is actually a square, with one corner--home plate--forming the basis of an ever-widening angle. The other three bases constitute the other corners of the square--tilted at an angle, from the viewer's perspective so that it looks like the shape of a diamond.

There is 90 feet of space between each base, although with the bases themselves it's probably more like 89 feet. Baserunners must touch a base in order to be safe, so the slight difference in distance can be crucial. Ninety feet was settled upon as an optimum balance between offense and defense. If it were any further, the runner would have to go too far to reach base safely. Any shorter, and he could reach base too easily.

The pitcher's mound is in the middle of the baseball diamond. Major League Baseball stipulates that the mound must be 18 feet in diameter, with the rubber precisely 60 1/2 feet from the furthermost tip of home plate. This distance was settled upon after a fair amount of tweaking in the late 1890s. The reasoning behind it was the same as the reasoning for the distance between bases; it provided an optimum balance whereby the pitcher could throw effectively but the batter still had a reasonable chance of hitting the ball.

The infield is positioned in a diamond shape because it gives the umpire an optimal view of the field. From his vantage point behind the plate, the foul lines stretch out along the first two sides of the diamond. That lets him gauge whether or not a ball is fair very quickly (aided by the foul ball poles at the far end of the field in the event of a home run), and allows him to make the correct call without a lot of dithering.

Technically, a baseball diamond should be built with home plate facing east. This keeps the sun out of the batter's eyes, since many games are played in the afternoon. (It also led to left-handed pitchers being referred to as "southpaws," since their left hand was positioned to the south.) Most major-league ballparks continue to adhere to this tradition--even those built in domes. One exception is Coors Field in Colorado, which doesn't face east.