Putting MLB Aging Theories to the Test on Star Players
Ballplayers aren't indestructible. Even the greats can't play forever, and there comes a time when they start to drift further away from the production that made them great in the first place.
We know why ballplayers can't play forever. Unlike Indiana Jones, both hitters and pitchers are done in by the years and the mileage.
As for when greatness starts to fade, well, that's the million dollar question. It also happens to be a question with plenty of answers, but no real consensus.
One of the more notable studies done on how players age was carried out by J.C. Bradbury and published in Journal of Sports Sciences. (He revisited it for Baseball Prospectus in 2010.) In his study, Bradbury concluded that both hitters and pitchers peak around the age of 29, or maybe more around 30 in contemporary times.
Mitchel Lichtman of Hardball Times had a beef with Bradbury's study in large part because it relied too heavily on players who enjoyed longer careers. He pointed out that "traditional sabermetric wisdom" says that players peak around the age of 27, and his own study concluded that modern players are likely to peak around the age of 28.
It's probably never going to be agreed on as to exactly when players reach their peak, but studies like these at least give us a good ballpark figure: It's somewhere between the ages of 27 and 30.
But what about the greats? Does the 27 to 30 rule apply to them, or are they special in some way?
That's what I wanted to find out.
The studies done on the aging patterns of ballplayers have been very much on the complex side. Those who follow in their footsteps will need to know how to handle statistics.
Fortunately for yours truly, the idea here isn't to follow their path. It's merely to see if the age 27 to 30 peak window has any relevancy to recent star players, and all that requires is a good enough sample size of star hitters and pitchers and a look at how their production was manipulated by the passing of time.
As for the ground rules, I defined the beginning of "recent" to be the year 1980. I borrowed this idea from Lichtman, who deemed everything that's happened after 1980 as the "modern era" because of "advances in medicine, higher salaries, and perhaps PED use."
The players I chose for examination were picked using Baseball-Reference.com's WAR as a measuring stick, but with some exceptions here and there made necessary by special circumstances. I ultimately ended up with a collection of 20 hitters and 20 pitchers whose names you should recognize.
Now then, let's get to it.
Using Baseball-Reference.com's Play Index tool—it will tell you the meaning of life if you ask the right questions—I drew up a list of the players with the best total WARs since 1980 and picked out 20 who fit the requirements of this sinister little experiment.
The experiment required players who were active starting at at least the age of 24 beginning in 1980 and who remained active through at least the age of 36.
I had to reject three players from consideration: Albert Pujols, Ozzie Smith and Ryne Sandberg.
Pujols was rejected because he's only played through his age-32 season. Smith's age-24 season happened in 1979. Sandberg didn't play in 1995, which would have been his age-35 season.
Excluding those three, I ended up with a sample size containing: Barry Bonds, Alex Rodriguez, Rickey Henderson, Cal Ripken, Jr., Wade Boggs, Chipper Jones, Ken Griffey, Jr., Jeff Bagwell, Frank Thomas, Larry Walker, Derek Jeter, Jim Thome, Barry Larkin, Scott Rolen, Tim Raines, Rafael Palmeiro, Tony Gwynn, Kenny Lofton, Alan Trammell and Manny Ramirez.
Mush their production together, and their WAR progression between the ages of 24 and 36 looks a little something like this:
For the record, the Bonds exception has to do with the absurd 11.6 WAR he compiled in his age-36 season in 2001. We know now that he wasn't playing on a level playing field.
Either way, you can see the significant drop that goes into effect at the age of 31, which isn't that far off from the age-30 danger zone that Bradbury hinted at in his study. The drop is also reminiscent of a study that FanGraphs' Jeff Zimmerman did in 2011, in which he also concluded that the age of 30 is right around when things start to get frightening.
The effect isn't all that different if the players with the 10 highest WARs in my sample size are separated from the players with the 10 lower WARs:
Here, you can see the players with the 10 higher WARs start to go into a sharp decline at the age of 30. The next 10 players enjoyed a rebirth after 30, but it didn't last long. They went into decline after turning 31.
Though he's not part of the study, it's worth pointing out that the decline outlined in the above graphs applies to Pujols. His 9.4 WAR in his age-29 season in 2009 was the highest of his career, but since then, his WAR totals have been trending in the wrong direction. He had a 7.3 WAR at age 30, a 5.1 WAR at age 31 and a 4.6 WAR this past season at age 32.
Bradbury's study relied on hitters who had played at least 10 years and compiled at least 5,000 plate appearances. Each player that went into my mixture fits that particular bill, but their combined star power was only powerful enough to push the danger area from about 30 to about 31.
So if you have a favorite hitter out there, keep a close eye on him when he crosses over into his 30s. Things are probably going to start going south soon after.
Choosing a sample size of 20 pitchers to put under the microscope wasn't as easy as choosing a sample size of 20 hitters. I'll admit that I had to make some concessions in order to get it done.
I started the same way I started with hitters, and that was to use Baseball-Reference.com's Play Index to dial up a list of the starting pitchers with the best WARs since 1980. The idea was to pick pitchers who were productive between the ages of 24 and 37.
That's not as easy as it sounds. Once you get to a certain point on the list, starting pitchers who actually managed to pitch continuously in the majors from age 24 all the way to age 37 are few and far between. A fair number of pitchers got hurt and had to miss a season. Quite a few others didn't last until they were 37.
This says a lot about how durable (or not durable) pitchers are. In the words of Los Angeles Dodgers chairman Mark Walter: "Pitchers break."
But as for the pitchers who did make the cut, the list includes: Roger Clemens, Greg Maddux, Randy Johnson, Pedro Martinez, Mike Mussina, Curt Schilling, Tom Glavine, Kevin Brown, David Cone, Andy Pettitte, Chuck Finley, David Wells, Mark Langston, Kenny Rogers, Jimmy Key, Bob Welch, Al Leiter, Kevin Millwood, Pedro Astacio and Rick Sutcliffe.
Mush them all together, and their WAR progression between the ages of 24 and 37 looks like this:
That downward spike at the age of 29 certainly looks odd and out of place. You can thank the guys on the bottom half of the sample size for that, as a handful of them didn't do so hot in their age-29 seasons. Wells and Astacio, for example, both posted negative WARs in their age-29 campaigns.
Things look drastically different if the top half of the list is separated from the bottom half:
Before experiencing a slight drop at age 30, the top 10 pitchers peaked at age 29, just like Bradbury said they should. They also peaked once again at 31 and refused to go quietly after a decline at 32. They were thus able to hold off Father Time better than the 10 best hitters of the last 30-odd years.
The bottom-10 players peaked at 30, but it didn't last for long. A sharp decline came at 31, and it was a mixed bag that trended mostly downwards after that. They couldn't enjoy the same kind of success around their mid-30s that the top 10 pitchers could.
Zimmerman and Bill Petti did a study on pitchers for FanGraphs in 2012 that sheds some light on why that may be. They found that starting pitchers start to lose velocity around the age of 28 and that the decline just keeps getting steeper and steeper on the other side of 30.
Less velocity means fewer missed bats and more sharply-hit balls in play, and such things make it hard to sustain success. But the top 10 group features the likes of Maddux, Martinez, Mussina and Glavine, who were successful pitchers even after they lost their velocity. The bottom group featured soft-tossers as well, but low-velocity dominance eluded them.
By and large, the charts show that star pitchers are going to ascend more gradually than star hitters. They will peak right around the 29 to 30 range that Bradbury referenced, but the peak isn't sustainable for very long and only really special pitchers are going to be able to hang around after it passes.
The methodology I chose for this study isn't foolproof. Other stats besides WAR could have yielded different lists of players and thus, different results. Also, some injury-ruined and/or subpar seasons went into my mix, which surely impacted the data.
The overall point, however, is that Bradbury was on to something when he found that modern ballplayers are going to peak around 29 or 30 and be in danger of declining afterwards. Though Lichtman disagreed, one of the charts he produced showed that modern ballplayers with 10 years of service time and 5,000 plate appearances under their belts are indeed likely to still be productive past the age of 28, but only for a couple years.
It makes total sense that star players would be able to survive the 27 to 30 danger zone, for we know that the best stars succeed because they have both talent and a superior ability to adjust as they go along. They should be able to succeed longer than the average ballplayer.
But if the 20 hitters and 20 pitchers I looked at are any indication, star power is only worth so much. It can help extend your career, especially if you're a crafty pitcher, but likely only by a year or two. After that, Father Time is going to be around the corner waiting to collect what he's owed.
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