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P2F Toronto Blue Jays

P2F

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Studying the baseball to find the ‘how’ of the home run surge

 

By Dr. Meredith Wills Sep 19, 2018

 

 

Baseball’s home run surge is redefining the game. Thanks to MLB’s Home Run Committee report, we now know why the home run rate went up, and my previous article showed what had changed. The remaining question is, “Howdid this change lead to the home run surge?”

Perhaps now we have an answer.

We already knew that it all comes down to the ball. MLB’s committee found that the spike in home runs was caused by a decrease in the ball’s aerodynamic drag. Basically, a hit at a given speed and launch angle travels farther if the baseball was made after 2015. However, they couldn’t find any physical difference to the ball, so there was no way to explain the change.

My earlier study found that difference: The laces on post-2015 baseballs are 9 percent thicker.

baseballcomp1-1024x554.jpg

Figure 1: Visual comparison of a pre-2015 baseball (left) and a post-2015 baseball (right).

 

 

However, thicker laces in and of themselves aren’t enough to explain a decrease in drag.

In order for the ball to move differently through the air, either the shape, surface, or “wobble” has to change. The Home Run Committee offered several theories along these lines. One was that the core—commonly known as the “pill”—could have become more centered, resulting in less “wobble.” (As an analogy, consider that a spiraling football travels farther than one that tumbles through the air.) Another was that the leather covers could be being processed differently, creating a smoother surface. A third suggested an overall increase in spherical symmetry; in effect, a rounder ball is able to travel farther.

I considered that third theory. In my original article, I postulated that thicker laces might lead to a more spherically symmetric ball. This stems from the idea that the “weak point” on a baseball is the seams, and therefore the most dramatic deviations from spherical symmetry should occur there. Since thinner laces aren’t as strong, they are more likely to stretch, producing greater “bulging” at the seams. The result would be a baseball that is less round. Conversely, thicker laces would lead to less bulging, creating a more spherical ball with lower drag.

To test this hypothesis, I again examined two samples of baseballs—twenty from the 2010-2014 seasons and twelve from April-May 2018. Using calipers, I measured each ball’s diameter at five points.

baseballcomp2.png

 

Figure 2: “Average diameter” measurement points vs. “seam-adjacent diameter” measurement points.

 

 

I came up with a baseline diameter for each ball by measuring across the center at the four widest leather sections and between the narrow strips perpendicular to those sections (one side of which has the commissioner’s signature.) Averaging these measurements gave me the ball’s “average diameter.” Since the seams are raised relative to rest of the ball, actual seam-to-seam diameters wouldn’t provide a viable basis for comparison. Instead, I measured diameters within about 2mm of the seams on each end and took the average (the “seam-adjacent diameter”.) A baseball with bulging seams would be expected to have a larger seam-adjacent diameter.

The graph below shows the difference between each baseball’s average diameter and its seam-adjacent diameter.

baseballcompgraph.png

Since every baseball is a slightly different size, I compared percentage differences rather than absolute ones. The blue lines indicate a larger seam-adjacent diameter, while the red lines show a smaller one. Any ball with a blue line is bulging at the seams, and the length of the line indicates by how much.

In every single case, the 2010-2014 baseballs had greater diameters near the seams, with an average difference of 0.66 percent (roughly 1/2 millimeter). While those in the 2018 sample also showed a larger average seam-adjacent diameter, it was much smaller (0.19 percent, or roughly 1/7 mm) and not systematic. These findings suggest that balls made after 2015 have less bulging at the seams, meaning they are more spherically symmetric, and thus have lower drag.

Since each baseball is made by hand and the diameters often vary by several millimeters from ball to ball, one would expect significant variability in the differences between average and seam-adjacent diameters. This means that the trend seen here is not enough to provide a definitive conclusion. (In technical terms, the results are not statistically significant.) However, the fact that all of the pre-2015 balls show bulging is telling. One could argue that, because they are older, the 2010-2014 balls have had more time for the seams to stretch, but this theory is inconsistent with the findings of the Home Run Committee (MLB Home Run Report, section 3.4). Rather, it appears that the thinner laces are “stretched” from the beginning, and remain so.

The source of this aberration may lie in the manufacturing process itself. According to the Home Run Report, the leather covers are moistened prior to being stitched in place, and afterwards the still-damp baseballs are “rolled between grooved wooden platens…to flatten the seams and maintain a spherical shape.” This suggests that, during construction, the wet leather dampens the red cotton laces. Unlike wet wool, which—regardless of stretching—generally returns to its original dimensions, air-dried cotton does not “spring back.” In other words, if wet cotton is allowed to dry under tension, it will remain stretched. Since thicker laces have greater tensile strength, one would expect post-2015 laces to stretch less under these conditions, leading to less seam-bulging and resulting in more spherically symmetric baseballs.

Since all that is needed to create the home run surge is a slight decrease in average drag, the ball doesn’t have to be perfectly round; it just has to be rounder.

We already established that the laces have changed. Since thicker laces appear to produce more spherical baseballs, we now have at least a viable explanation as to how this one largely overlooked change took us from 4,186 home runs in 2014 to a record-high 6,105 in 2017—the most dramatic offensive increase this game has ever seen.

 

https://theathletic.com/533397/2018/09/19/studying-the-baseball-to-find-the-how-of-the-home-run-surge/

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Pendleton Vancouver Canadians

Pendleton

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Sano comments on the incident

"Guess what, I have flaws. What are they? Oh, I don't know. I sing in the shower. Sometimes I spend too much time volunteering. Occasionally I'll hit somebody with my car. "

Spanky__99 FCL Blue Jays

Spanky__99

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Sano comments on the incident

"Guess what, I have flaws. What are they? Oh, I don't know. I sing in the shower. Sometimes I spend too much time volunteering. Occasionally I'll hit somebody with my car. "

 

lol

DigitalRock FCL Blue Jays

DigitalRock

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Sano comments on the incident

"Guess what, I have flaws. What are they? Oh, I don't know. I sing in the shower. Sometimes I spend too much time volunteering. Occasionally I'll hit somebody with my car. "

 

That's awesome.

Thaddeus Malice Prep Ball

Thaddeus Malice

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This is crazy.

 

https://www.fangraphs.com/blogs/the-dodgers-might-be-in-actual-legal-trouble/

 

And this is hilariously Ill advised.

 

One particularly remarkable document shows that Dodgers executives in 2015 went so far as to develop a database that measured the perceived “level of egregious behavior” displayed by 15 of their own employees in Latin America. That is, using a scale of 1 to 5—“innocent bystander” to “criminal”—front-office executives assessed their own staff’s level of corruption. Five employees garnered a “criminal” rating."

 

We can all agree that analytics are wonderfully useful. For those who have plans of participating in international organized crime, however, please note that crafting charts to depict one’s level of criminality is unwise — as is openly discussing one’s own personal mafia.
G-Snarls Cooperstown

G-Snarls

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Game 1 SP's

 

Verlander vs Sale

 

Kershaw vs ???

 

One of these 4 teams doesn't have the quality SP that the others do...

Orgfiller All-Star

Orgfiller

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Dodgers are starting Freese at 1st over Muncy in Game 1 with Gio on the hill...

 

Muncy posted a 141 wRC+ vs. LHP this year. This is insane.

 

Freese put up a 140 wRC+ over more PAs and is a career 134 wRC+ hitter against lefties. This isn't that shocking of a move.

Boxcar All-Star

Boxcar

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Does Didi get nontendered? It's his throwing arm. He might be out the whole season.

 

He's not going to be out the whole year, PP recover much faster that pitchers. There's a 0% chance a 4 WAR ss is going to get non-tendered unless they arrange to re-sign Didi at a lesser price and I have no idea why he'd agree to that.

Ray FCL Blue Jays

Ray

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He's not going to be out the whole year, PP recover much faster that pitchers. There's a 0% chance a 4 WAR ss is going to get non-tendered unless they arrange to re-sign Didi at a lesser price and I have no idea why he'd agree to that.

 

Gleyber Torres was out 9 months for his non throwing arm. Might be looking at 10 months for Didi because it's his throwing arm.

 

Not that the Yankees are in any shortage of funds, but if I'm them, I'd throw money at Machado and use the $12M towards a Harper or Kershaw who'll provide more value than Gregorious would in half a season.

Dr. Dinger GOAT

Dr. Dinger

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He's not going to be out the whole year, PP recover much faster that pitchers. There's a 0% chance a 4 WAR ss is going to get non-tendered unless they arrange to re-sign Didi at a lesser price and I have no idea why he'd agree to that.

 

Which position players have returned in significantly less than a year? Miguel Sano missed an entire season. Matt Wieters and Corey Seager, same thing.

Boxcar All-Star

Boxcar

Old-Timey Member
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Which position players have returned in significantly less than a year? Miguel Sano missed an entire season. Matt Wieters and Corey Seager, same thing.

 

Even assuming he misses the entire year, non-tendering him would be unwise.

Dr. Dinger GOAT

Dr. Dinger

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Even assuming he misses the entire year, non-tendering him would be unwise.

 

That's what a cheap organization would do. However the Yankees universe loves Didi, so they'll probably sign him to a multi-year contract extension which factors in 15-20% of a season in 2019.

Dr. Dinger GOAT

Dr. Dinger

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Also, watching this TBS exclusive playoff coverage reminds me how much I dislike Ron Darling. He's just a half notch above Dennis Eckersley and Harold Reynolds. Darling actually had a whole rant about how D.J.L.M. was the Rockies MVP, and without caveats. Because apparently, being an average player and not getting attention on a team with multiple superstars actually means that you're the secret sauce.
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