The Ball Is (Maybe) Juiced Again
Over the last couple of years, the massive home-run spike that began in the second half of 2015 has been the biggest story in baseball. Jeff just noted the other day that home runs are once again trending up quickly, even relative to the new recent norms, and the home-run era is showing no signs of leveling off.
In trying to find an explanation for the sudden and massive increase in home runs, the ball has always seemed like the most reasonable explanation. No one has done more work on whether the ball is at the center of the home-run spike than Ben Lindbergh, who did a deep dive on the issue at FiveThirtyEight last summer, then gotaccess to some results of MLB’s internal study on the issue a month ago, putting something of a damper on the ball as the culprit.
Today, though, Ben is back with a new piece, and based on some research commissioned by Mitchel Lichtman, there again appears to be some evidence that the ball has changed the last few years.
The newer balls have higher CORs and lower circumferences and seam heights, which would be estimated to add an average of 7.1 feet to their distance, equivalent to the effect we would expect to stem from a 1.43 mph difference in exit speed. Although those differences don’t sound enormous, Nathan has noted that “a tiny change in exit speed can lead to much larger changes in the number of home runs.” Last July, he calculated that an exit-speed increase of 1.5 mph would be sufficient to explain the rise in home runs to that point, which means that the 1.43 mph effective difference that Lichtman’s analysis uncovered could comport almost exactly with the initial increase in home runs. Lichtman calculates that a COR increase of this size, in this sample, falls 2.6 standard deviations from the mean, which means that it’s extremely unlikely to have happened by chance.
Alan Nathan, the foremost expert on baseball physics out there, did offer a response on Twitter that this is still not an open-and-shut case.
The effect of a small change in seam height on fly ball distance may be overstated in the article. See https://t.co/YcLUhtvFUB, Fig. 5. 1/2 https://t.co/iooacinKUz
— Alan Nathan (@pobguy) June 14, 2017
The effect of a small change in seam height on fly ball distance may be overstated in the article. See https://t.co/YcLUhtvFUB, Fig. 5. 1/2 https://t.co/iooacinKUz
— Alan Nathan (@pobguy) June 14, 2017
But with nearly every other reasonable cause for the spike in home runs, and the speed at which things changed after 2015, it’s still difficult to reconcile current home-run levels with anything besides some change in the ball. Ben and MGL’s data provides a bit more evidence that the ball is maybe at least part of the explanation. I definitely encourage you to read their entire piece, as it’s some of the best baseball research done in the public sphere.
Dave is the Managing Editor of FanGraphs.
Call me a conspiracy theorist, but when Alan Nathan was *paid* by MLB to research if the ball was juiced, I have to be a little skeptical of his findings.
Normally you should be weary in this situation of paid shills, but I think this was just a side gig and temporary one at that for the guy. I doubt it’s worth his reputation.
I suppose, but I feel he could also cover his tracks by simply saying, “Hey, I used baseballs that MLB supplied me.”
He didn’t even use any baseballs, he was only given a bunch of numbers by MLB. He didn’t collect any of his own data (nor was he paid to or supposed to).
and Ted Wells investigation of the Patriots was impartial too
He’s done way more research at the behest of public journals, like FanGraphs and THT, than he has for private sources.
Also keep in mind that he only analyzed the data that MLB gave him, and his analysis is publicly available. All the work he was paid to do is publicly critiqueable, and almost no one has critiqued it.
What I would be most suspicious is that data that was given to him. MLB paid him to analyze *their* data, not collect his own, so I wouldn’t take that dataset with a grain of salt, far moreso than the analysis of that data
MLB doesn’t have a skin in this game. Don’t worry about it!
It’s either a juiced ball or bat. No other theory (new undetectable PED, flyball revolution, wave of elite prospects graduating, moving fences in/small ballparks, climate) could have happened within a month to explain the immediate spike which turned into the new normalcy for 2 years
Can I just point out how much FanGraphs writers seem to have whipsawed back and forth here? It seems like the comments section maintained more reasonable methodological skepticism than the writing above the fold on this one — maybe a little introspection about recency bias, overweighting the conclusiveness of the last seemingly data-laden article you’ve read, is worth considering.
I would really hope that Fangraphs writers are free to hold their own beliefs. At the point where they are all writing the same article, there will be no reason to come back to FG.
come on guys, we all know that homeruns are up because Daniel Murphy and Yoenis Cespedes started hitting more balls in the air and they learned how to do it over the all star break and immediately taught it to everyone else the very next day.
Daniel Murphy and Jeff Mathis are the prophets leading baseball into the brave new future.
It was Marlon Byrd that taught Murphy, and Byrd has been popped for PEDs, so therefore PEDs are to blame!
As much as I’ve been a proponent of team “It’s juiced”, the data shown in Ben’s latest has no error bars, no statistics, just mean values. Total lack of scientific rigor… a little hard to draw any real conclusion from it.
http://imgur.com/cI6OchU.jpg
for anyone curious what this would look like with error bars.
What do the error bars represent? Standard deviation? SEM? Because if it’s deviation, I would argue that you can see significant differences in COR and circumference.
STDEV. IMO, COR is the only statistically significant finding… does not yet fully explain what’s going on, but nice to see some evidence?
But if it was just a one-time change to the ball, why are HRs up so much again in 2017?
…because they kept making them that way?
All else equal, “keep making them that way” would mean HR rate would be about the same in 2017 as it was in 2016. If it was just a one-time change to the ball, then something else must be different, and Mr. Santana was simply inquiring what that might be.
And hitters have adjusted to the juiced ball by focusing on hitting more fly balls.
THIS is the question every juiced-ball believer ignores. One of the big ones, anyway.
Ben’s article covers some of this at the end, explaining how it worked at the end of the dead-ball era.
In 1919 a new kind of wool was used for the ball, and it was bouncier. Offense went up.
In 1920, the dead ball era ended and regular switching out of baseballs began. This is a big help to the hitter, and offense goes up further.
In 1921, the previous two things had been true for 1-2 years, and hitters started to adapt to the fact that the returns on trying to swing for power were better, so more did. Offense went up even further, and Babe Ruth started Babe Ruthing. Others followed.
What’s going on is probably a confluence of many things: changes to the ball, even ones within MLB’s specs which are pretty loose tolerances, changes to batmaking, and changes to hitters, especially in 2017.
As the returns on focusing on power have improved, more hitters have chosen to do so, hence power numbers increase further. This explains why the power explosion didn’t start in AAA until this year (they dont use the same ball from the same manufacturer, but their incentives changed, so more players are focusing on power).
It’s almost certainly true that what’s going on is the result of many factors, the question of whether the ball has changed only answers what began the cascade, because they are all factors.
This is very clearly addressed every time the important question is brought up. 1) SSS 2) Players are adapting to the juiced balls. Hardly a point of contention for me.
A change in seam height would definitely change a pitcher’s comfort and rotation on breaking balls. Have there been any studies relating the home run binge and breaking ball usage?
Higher spin rates (breaking balls) perhaps leading to longer fly balls combined with a potentially “juiced” ball makes sense to me.
who cares I LOVE THE LONG DONGS
It’s bizarre that people keep focusing on the 2nd half of 2015 vs. the 1st half. The 1st half of that year had an almost identical rise from the previous half’s HR/batted ball. If there’s ANY “juiced ball” conclusion to draw from that season, wouldn’t you place the change at the start of the year?
When there’s such a confounding premise, I tend to write off the whole line of reasoning.
And anyone who thinks that a juiced ball is the ONLY logical explanation for soaring HR rates, just hasn’t looked at enough data on changes throughout baseball history.
1st half 2014 HR/FB 9.8%
2nd half 2014 HR/FB 9.1%
1st half 2015 HR/FB 10.7%
2nd half 2015 HR/FB 12.1%
1st half 2016 HR/FB 12.9%
2nd half 2016 HR/FB 12.7%
To date 6/14/17 HR/FB 13.5%
IFFB Rate has stayed steady (9.5%-9.7% – 2014-6/14/2017)
Maybe it’s combinations of the new strike zone and the new ball and the incentive to tweak your swing to hit the new ball from a different angle?
I’m not sure, but I guess you’re agreeing with me, since you show consecutive HR/FB spikes in both the 1st and 2nd half of 2015.
I don’t disagree with anything you said. I wanted to show the increase that you mentioned (I have no choice but to agree with you on that).
As for the rest of the data, it’s there to show the continuous climb from one season to another.
The last part is me throwing darts, hoping that one of them might stick.
I see the spike. Certainly not what I would call bizzare.
Wouldn’t the increase from 2nd half of 2014 to 1st half of 2015 be due to regression to the mean from the decrease in the 2nd half of 2014?
Most likely, it is. I found it really interesting though, that the 2nd half of 2014 – 9.1% and the 2nd half of 2015 – 12.1%, HR/FB increased 3%. That seems like a very large increase, too me.
Folks who want a smoking gun for every significant change should try to explain this annual sequence in HR/batted ball
1969 … 2.84%
1970 … 3.10%
1971 … 2.59%
1972 … 2.41%
1973 … 2.74%
1974 … 2.33%
1975 … 2.38%
1976 … 1.96%
1977 … 2.95%
1978 … 2.41%
1979 … 2.77%
1980 … 2.46%
HRs soared in 1969 and ’70 with the lowered mound, etc. But the ’72 rate was the lowest in 20 years, except for 1968.
The DH began in 1973, so that spike makes sense. But the ’74 rate dropped back below ’72, and then ’76 was the lowest in 30 years.
1977 brought a 2-team expansion, and they both had terrible pitching, so that huge spike makes some sense. But they still had terrible pitching in ’78, and the rate plunged. Then it went up again, and down again.
There are always so many factors at play, including randomness. It’s rarely one thing causing the bulk of a change.
Changing the mound, adding a DH and adding teams are all going to increase volatility as players adjust. The difference this time is that there have been no public changes made to the game or its talent pool.
I’m not sure what you mean by “public changes.” I would rather speak of forces out of the batters’ control that would spur them towards change. And in that vein, we have the explosion of extreme infield shifts in the last 5 years or so, along with data-driven outfield positioning. We also have an unprecedented degree of emphasis on selecting pitchers for their strikeout ability.
I’m not asserting that batters’ choices explain the bulk of the HR increase. But we’ve always known that choice was ONE factor in the HR rate. I have no doubt that Stan Musial could have hit 40 HRs a year with a .280 BA, if he didn’t think it was better to bat .340 with 25 HRs. What I’m saying is, the variables in that choice equation have changed more in the last few years than at any time since the start of the “live-ball” era. Musial today wouldn’t really have the option of batting .340.
’76 looks very strange there. That said, trying to compare the 70’s to today is a foolish process. There is so much more information, coaching, a larger talent pool and many other factors that todays game have and they did not then.
Lower seam height could affect pitches movement and I imagine reduce the effectiveness of 4 seam fastballs . Lots of breaking and off speed pitches are feel pitches and any changes there could hurt somebpitchets slow to adjust. I still think The COR is elevated and the shrinking strike zone us also having an impact.
With MLB in the gambling business congress needs to investigate. Balls can be changed at will to influence team and game outcomes over a large number of games. We need a 3rd party to keep it honest, or at least far more transparency than MLB is willing to provide
Hideki Irabu the pitcher that would wear magnets under his uniform……RIP
http://www.arctic.io/explorer/4Xa5A//4-N90-E0
GIVE THIS LINK A QUICK LOOK…
I plugged all of my values into Dr. Nathan’s own equations in that paper he cited, wherein they tested balls of various seam heights. If anything, we understated the effect of the lowered seam height, not overstated it. We said that lowering the seam height from .04089 to .03843 inches would result in an increased fly ball distance of 2.9 feet.
According to Dr. Nathan’s equations, it would be around 5.1 feet.
I estimated the coefficient of drag for the two respective seam heights, from the old and new balls, using his equation. Then I plugged those coefficients into his equation for distance versus coefficient of drag formula. That produced a difference of 5.1 feet.
So I don’t know why he says we may have “overstated” the effect.
Great MGL, now you did it. You broke physics 🙁
I don’t understand why we are not talking about the cores of the baseballs. Anyone who played enough baseball or even slow-pitch softball knows that not all balls are created equal in a given box. Some balls are soft or mushy and some are harder. That is what really influences how far a ball flies.
The study in this particular sub-thread doesn’t, but all the “comprehensive” juiced ball studies all look at the Coefficient of Restitution of the balls, which is basically directly related to the cores.
My aerodynamics is a little rusty, and I might be missing something from Dr. Nathan’s methodology, so bear with me…
For a spinning baseball, the seams should work as turbulators that help keep the flow attached to the spherical surface, which should have the joint effect of increasing lift due to magnus effect, and offsetting the static drag penalty of having bumps on the surface. How much of an effect the seams have depends on the exact geometry and spin rates, but I haven’t done the math, so who knows?
From what I can tell, C_l and C_d of the baseballs in the cited experimented were not directly measured or analytically determined, but were the output of a parameter estimation exercise to match experimental flight distance data. The paper doesn’t specify, but I assume they used some kind of standard ballistic model, which is probably pretty close to reality, but it does introduce the risk of more uncertainty due to oversimplification.
“The average lift and drag coefficients for each ball were found using the measured launch conditions by adjusting Cd and Cl until the predicted flight time and carry distance matched experiment.”
In a sense, the close correlation shown in Figure 5a is a bit contrived, since it is the result of an optimization routine. And I believe that in the actual physical model, the relationship between seam height and launch distance should not be linear.
This is not to criticize the research, but to warn that extrapolating/interpolating drag and estimated flight distance using that model may not yield reliable results.
What about the recent report on increased launch angle?
https://www.washingtonpost.com/news/fancy-stats/wp/2017/06/01/mlb-home-run-spike-shows-statcast-science-is-more-potent-than-steroids/?utm_term=.5742d3a4513e
This “issue” is never going to be closed. Juiced balls are not the kind of thing that can be dis-proven. The only way it could be proven is if somebody fesses up to something and MLB has millions of incentives to make sure that doesn’t happen, so it won’t. It would never happen – look at how difficult/possibly illegal it was for the NFL to prove that the Patriots drained air from footballs for a single game. This is like that… but even harder to prove. If the media wasn’t so anti-Patriots, I bet they would have gotten off without any repercussions. When you consider all of the combined interests of the narrative of players evolving and growing by Statcast data, there is no chance that the HR surge is attributed to outside factors. I think MLB learned from their PED witch hunt which kind of destroyed their brand.
This is just a plea to not pick a side. Nobody is ever going to be right, despite what some of us will claim. I know it is a lot easier to adopt someone else’s canned argument as the truth but it is never that simple in reality. I would bet that it is one part both: juiced balls led to more home runs, which led to swing changes when players learned that the ball changed. OK, so maybe that is 3 parts ball and 1 part swing change, but you get the idea…
I can’t help but say I told you so. It was very obviously the ball the whole time.
Here’s another sequence to ponder:
1) From 1982-84, HR per batted ball was stable around 2.7%.
2) Then came 3 years of increase, reaching 3.7% in 1987.
’87 saw the biggest increase, so that’s the year everyone talks about, but the prior 2 totaled as much gain as ’87.
3) And then, poof — in ’88 it fell back to the ’84 level, in one fell swoop. And then was stable through ’92.
Comparing 3-year averages, 1985-87 vs. 1982-84 saw the biggest change since WWII, to that point.
But the ’88 plunge is still the biggest one-year change, by far, in the same span.
There was no expansion in these years.
There was a strike-zone change in ’88, but it’s hard to pinpoint its effects, in theory or in results. The top of the zone changed from “armpits” to “midpoint from top of shoulders to top of pants.” BB% saw a one-year dip of 0.8%, but SO% also dipped by the same amount, and BB% headed back up the next year. And even if the strike-zone change explained the drop in HRs, what explains the 3-year rise?
Here’s my point: I don’t deny the possibility that the ball has changed in recent years. But I don’t think the study cited here is conclusive proof of a change, and it’s certainly not proof that such change is the main thing driving HRs upward. I don’t think it’s possible to form a simple narrative to explain the current trend, or many others seen in baseball history.