Baumann: Could the dejuiced baseball send MLB into another deadball era?

From SABR Michael Baumann at The Ringer on October 15, 2019:

Since mid-2015, MLB’s game-used baseballs have come off the bat as if shot out of a cannon, as a more aerodynamic ball with a better-centered core has led to record leaguewide home run totals. It’s been empirically proved that both the ball and the resulting run environment have changed, but the league has been cagey about the cause. That’s understandable from its perspective, as MLB owns ball manufacturer Rawlings: A substantial change to the baseball would imply either an inability to ensure a consistent equipment-manufacturing process or a deliberate decision to change the conditions of the game without telling anyone.

Whatever the cause, the juiced ball is the most impactful and controversial equipment change in recent baseball history. But just as suddenly and inexplicably as it arrived on the scene, the juiced ball appears to have disappeared in the past few weeks.

Anecdotally, pop flies that carried over the fence for the past few years have begun to die at the warning track. Rob Arthur of Baseball Prospectus compared the drag coefficient of the baseball after the division series to the last week of the regular season and found the largest week-to-week change this season by far, and a ball that grabbed the air more than it had at any point since 2016. Given park effect, launch angle, and exit velocity, Arthur calculated that there should have been 67 home runs hit in the divisional round, when in reality there were only 43. Included in the missing 24 were three balls that would have had a 95 percent chance or better of reaching the seats in the regular season. And while the cold weather of October is an obvious place to look for an explanation, Arthur pointed out that at the time he performed his study, the average 2019 postseason game had actually been played in warmer conditions than the average 2019 regular-season game.

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Originally published: October 15, 2019. Last Updated: October 15, 2019.