Field Dimensions
The infield is identical everywhere and the outfield is not, which is the only major sport where that is true.
What it actually is. The infield is fixed: ninety feet between bases, sixty feet six inches to the rubber, seventeen inch plate. The outfield is not regulated beyond minimums, so every park has a different distance to the fence, a different wall height and a different shape. Fenway's left field wall is thirty seven feet high at 310 feet; Coors Field's center is 415 feet at altitude.
What somebody who knows the game gets out of it. Park factors exist because of this, and they are one of the strongest arguments for the numbers this site computes rather than recites. A hitter's raw home run total is partly a fact about where he plays half his games, so OPS+ and ERA+ adjust for it and wRC+ does too. Ignoring park is how you end up believing Coors Field hitters are better than they are and how Petco Park pitchers get contracts they should not.
The numbers worth knowing. Fences typically run 310 to 340 feet down the lines and 390 to 420 to center. A park factor of 110 means roughly ten percent more runs score there than in a neutral park; Coors has historically run well above that and the pitcher friendly parks well below.
What people get wrong about it. Altitude matters more than distance at Coors, and not only for home runs: thin air also reduces breaking ball movement, which is the effect people miss. The humidor was installed to address the ball itself and it changed the park meaningfully without making it neutral.
At Little League and travel ball. Youth field sizes scale by age and by sanction, which is one of the most confusing parts of travel ball for a new family: an 8U field, a 10U field and a 12U field have different base paths, mound distances and fence distances, and USSSA and Little League do not always agree on them. The travel section of this site lists the dimensions by age group for exactly this reason.
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