Arthur: The rocket ball has disappeared in October

From SABR member Rob Arthur at Baseball Prospectus on October 10, 2019:

On Monday, in game four of the NLDS, Max Muncy stepped up to bat against Nationals closer Sean Doolittle. On the fourth pitch, Doolittle left a 94 mile per hour fastball hanging over the center of the strike zone, and Muncy took a monstrous cut. The ball left the bat at 107 miles per hour on a 32 degree angle relative to the ground: a perfect home run trajectory. “That ball was absolutely crushed,” exclaimed Ernie Johnson after the play.

Then something unexpected happened. In a season with more than 6700 dingers, when a less air resistant ball has combined with stronger hitters to produce the highest home run rate in history, this fly ball wafted back to the warning track and fell into Michael Taylor’s glove. Muncy looked up to the sky, smiled, and shook his head.

Variations of this scene have played out a dozen times so far this October. The baseball that was rocketing over the fence in the regular season is gone, replaced by something more reminiscent of the low-homer days of 2016. Evidence from MLB’s tracking systems shows a massive change in the ball’s air resistance so far in the playoffs. And unlike previous season to season variations, this difference is much harder to explain by random manufacturing changes.

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Originally published: October 10, 2019. Last Updated: October 10, 2019.