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Mound Visit: What would a dejuiced ball mean? ☕


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Dario Agrazal allows a home run. -- AP

The World Series kicks off Tuesday, a final hurrah before the 2019 baseball season and a rather enjoyable postseason come to a close. The Astros and Yankees, in particular, put on a very compelling series that was ultimately decided by three fly balls. The first was Jose Altuve's Game 6 home run. Obviously. The second was Carlos Correa's walk-off in game two. The third one was not a home run, although it probably should have been.

Trailing 2-0 in the fifth inning of game three, Didi Gregorious launched a fly ball deep to right that looked good off the bat, but died at the wall:

We watched fly balls hit like that leave the yard all season long, but Gregorious fell a few feet short. This was not just one odd non-homer, either. The home run explosion came to a screeching halt this postseason.

In the regular season, there were 9,290 batted balls Baseball Savant qualified as "barrels." These are balls that were hit with a high exit velocity and a quality launch angle. Of those 9,290 barrels, 5,536 turned into home runs, a rate of 59.6%. In the playoffs, just 66 of the 131 barrels have been home runs, a rate of 50.4%. Barrels do not take into consideration the quality of the pitcher on the mound. Yes, the sample size is small, but the stage is large, and a near 10 point drop is telling. By Baseball Prospectus author Rob Arthur's estimate, by Oct. 10, there were 43 home runs hit, when in the regular season, there would have been 67.

And it's not just because of the October weather. Yes, fly balls do not travel as far in colder weather, but not by that much. With every 10 degree increase in Fahrenheit, the ball travels an extra 2.5 feet. The Cardinals' analytics department concluded the ball is traveling 4.5 feet shorter than it did in the regular season. So while the weather is playing a small role, it does not explain the drastic drop-off.

It's indisputable the ball was altered again. Commissioner Rob Manfred insists they are the same balls as the regular season, but they aren't performing the same. The term "juiced baseballs" has been thrown around these last few years, so it does not hurt to explain why they are "juiced." In 2018, the MLB Home Run Committee found the drag of the ball decreased in 2016 and 2017. One of the main reasons why was the laces were thicker, making the ball more spherical and more aerodynamic. There was even less drag on the ball in 2019, and Dr. Meredith Wills deduced it is because the seams are lower and the texture was smoother.

But the ball has had more drag in the playoffs. In fact, the ball has not grabbed this much air at any point since 2016. From Arthur:

Michael Baumann of The Ringer wrote about how a dejuiced ball would impact hitters across the league. Let's take the same approach from a local angle. What would it mean for the Pirates if the ball was dejuiced? This is going to be a two-part Mound Visit, focusing on just pitchers today. Tune in next time for the hitters.

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