Arthur: Baseballs are more consistently juiced than ever

From SABR member Rob Arthur at FiveThirtyEight on September 19, 2017:

We used to think of the steroid era as the heyday of home run hitting, but our mental image of a juiced-up behemoth crushing the ball needs updating. This year is poised to easily be the most homer-happy on record — and not because of altered player physiques, but rather thanks to physical alterations to certain batches of baseballs that make them fly more freely through the air. What’s more, recent data shows that these less-air-resistant balls probably make up a larger share of all MLB balls today than they did even earlier this season, meaning the game is now consistently being played with a ball that travels farther than usual.

MLB has denied making any intentional changes to the baseball, noting that testing finds the baseball still within established standards. But those specifications are extremely wide, allowing for massive variation in fly ball distance and corresponding shifts in home run rates. If MLB only rejects balls when they lie outside of the standards, there could be wild differences in air resistance between pairs of baseballs.

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Originally published: September 19, 2017. Last Updated: September 19, 2017.