Are Player Types Aging Differently Now?

At ESPN, they recently wrapped up their prospects week. I thought I’d zag from that zig, however, and instead wrote a piece for Insider about 30-year-olds and how they’ll age. Using some research from Jeff Zimmerman on aging by player type, I tried to spot some 30-year-olds who are about to go into the tank, and some that might age better than we expect.

But while working on the piece, I asked Zimmerman to update the research on player-type aging, starting in 2005. That’s the year baseball stiffened their steroid policy. Here’s something strange: in this, what we might call the “post-PED era,” it appears as though certain player types have begun aging in an entirely different way.

First, the original aging curve. It illustrates how different groups aged by overall runs production, which includes defense, baserunning, and offense. Zimmerman detailed the delta method he used for the aging, but it’s basically matched pairs with harmonic mean work included.

From the sample of all players going back to 1950, Zimm identified three specific player-type groups, as defined below.

  • Fast players were those who’d recorded 25 or more stolen bases and eight triples early in their career.
  • Young Old players had hit more than 20 homers, struck out more than 15% of the time, and walked more than 5% of the time at a young age.
  • Players with No Plate Discipline walked less than 5% of the time and struck out more than 20% of the time.

Here’s the aging curve for those players, as it appeared in 2011:

types_medium

It seems to fit with the prevailing wisdom in baseball. Fast players age well because they can add value on the basepaths and in the field. Young Old players age well because they’ll add value with power and patience even as they age. If you have no plate discipline, you don’t have walks to fall back on as your bat slows. So, that seems fine.

Now fast forward to the aging curves as run since 2005.

AgingPlayerTypes

Hold on. This is all backwards. What’s going on with the No Plate Discipline guys? Why are they aging best now instead of worst? And what happened to the Young Old Player Skills guys? They flipped sides. Is baseball on its head?

We know baseball has changed, just from looking at the box scores and the power leaderboards every night. But we first have to take a careful look at these curves before we run screaming to the hills.

For example. The No Plate Discipline guys do age “better” at the end. But they age worse at the beginning. They basically enter the league as meh players, and continue being meh as they go on. Also, the sample is smaller. The other curves have more than 30,000 plate appearances in most of the buckets. The No Plate Discipline curve averages around 10,000 in the middle.

And lastly, if there’s a survivor bias here — and there is in these sorts of curves, it’s almost impossible to remove from the process — it could affect the No Plate Discipline group more than the other two. If you have no plate discipline, and the rest of your game begins to suffer, you lose your spot on the roster. And then your bad stats don’t pull the curve down.

So there are a lot of reasons to believe that the No Plate Discipline curve is a red herring. Teams should not be lusting after Evan Gattis because of his poor plate discipline suddenly.

But there’s still the matter of the Young Old player curve dropping to the bottom of the pack. And the caveats from above don’t apply to that group. From age 25 to 35, the buckets in that group average 27,000 plate appearances. That seems a decent sample.

And if you can take a walk, you’ll stick around a little longer. In the Young Old grouping, the bracket from 35-39 averages 22% of the plate appearances of the 25-35 group. In the No Plate Discipline grouping, the 35-39 year old bracket averages 15% of the plate appearances of the younger group. So there’s less of a survivor bias effect, maybe.

So why would today’s three-true-outcome guys be aging worse than yesterday’s? We only have speculation at this point, but we do know the player types and what has changed.

It’s tempting to point to power being down around baseball and say that we must be getting less power from older players. But qualified batters over 35 averaged a better isolated slugging percentage from 2005 to -15 (.159) than they did from 1990 to -05 (.149).

That isn’t to say that baseball isn’t skewing younger. Players over 33 are producing less than they ever have before by raw numbers and by the piece of the pie. Look at this graph from Ben Lindbergh:

under30warp

So, despite their power and patience, older players with young old skills are producing less, and that holds with the general trend in the population. Maybe it’s a quirk of how we measure defense, since this time frame includes the birth of Ultimate Zone Rating in 2002. Or perhaps it’s the rise of defensive measurements that have better put a number on the way these players lose value as they plod their way through their 30s.

Of course, a more insidious reason is still possible. It’s possible that certain substances were helping the three-true-outcome sluggers stay on the field longer in order to take advantage of their power and patience advantage for a longer period of time. Now that they don’t have those substances, the more naturally athletic players are aging better.

But we don’t really know, for one, how many players are really using right now. And how many used in the past. And if one player type had more to gain from using than others. And what exactly the role of defensive metrics is in this change in aging curves.

It’s interesting that the Young Old player — the Three True Outcome Guy — may not be aging as well, though. That would mean something about the future of the game, how the game will look, and what players will be most valued in future free agent markets.



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Graphs: Baseball, Roto, Beer, brats (OK, no graphs for that...yet), repeat. Follow him on Twitter @enosarris.


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NickChristy
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NickChristy
3 months 3 days ago

The reasons you point out for the No Plate Discipline graph being a red herring all existed during the steroids era. So what has changed? It’s not like there wasn’t a survivors bias then also..

jdbolick
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Member
3 months 3 days ago

The NPD guys would also need to have a smaller percentage of the total PA pool at the end than in the beginning or middle to demonstrate a difference in survivorship.

Regression is Mean
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Regression is Mean
3 months 3 days ago

Analytics has changed. In the SABR, post-Moneyball era, guys with little discipline aren’t getting the same leash and deals they used to. Ruben Sierra would not have had that many PA’s if his career started in 2006 rather than 1986.

rosen380
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rosen380
3 months 3 days ago

Siera:

As a 20-22 year old he put up a .302 OBP with a 98 wRC+… similar to Jeff Francoeur and Jay Bruce. Both of those guys go chances beyond that to try and show their value despite low OBP%

Shirtless Bartolo Colon
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3 months 3 days ago

Guys with ZERO plate discipline age the best of all ;)

Big Daddy V
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Big Daddy V
3 months 3 days ago

Are older players worse, or is management just obsessed with younger players?

John Walsh
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John Walsh
3 months 3 days ago

Couple of thoughts:

The first two graphs are not really comparable. The older one has all curves starting from the same point at age 21, the second one has them all at the same point at their peak. If you take the first graph and place all curves such that they have 0 value at peak, then the ageing (post-peak) behaviour will not look so different among the different player types.

Also, given the jagged curves in both plots, I’m wondering about the error bars around those curves. Perhaps, the differences shown are not even significant. It would be interesting to see those curves replotted as bands which show the uncertainties.

Bip
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Member
Bip
3 months 3 days ago

I agree, as presented it is very hard to tell what is really going on, and I think this is a topic that deserves a more exhaustive investigation.

jfree
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jfree
3 months 3 days ago

Hard to make conclusions when the two graphs have pretty clearly been adjusted differently. The first graph uses age-21 or so as a baseline for all the data subsets and then adjusts from there. The second seems to use a different age-baseline (peak age for that subset) for each subset.

Charlie Hustle
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Charlie Hustle
3 months 3 days ago

The position of the curves, relative to each other, is dependent on the starting point. In the top graph, the starting point is age 21. In the lower graph, everything more or less flows from age 24 onward. Just eyeballing it, there is a steeper decline (average of 5+ runs/year) beginning at age 29, whereas the curves are much flatter between ages 24-29 (about 1 run/ yr decline). Therefore, if you really what to compare how the different groups age, it might be helpful to put everyone on equal ground at age 29 (when the decline becomes significant), and observe how the graphs flow from there. If you did this, you might see that from age 29 onward, the young-old and no-plate-discipline age similarly, and that the fast players decline more rapidly.

tz
Member
tz
3 months 3 days ago

Great point. Probably the best way to make this point of the article clear is to do show the results like this:

1. A chart showing the aggregate aging curves using the older data vs. the updated data.

2. A chart showing the ratios by age of:

(runs production of the group)/(aggregate runs production)

for each group, from the older data.

3. The chart in #2, but using the newer data.

Any shift in the relative aging curves would be apparent when comparing graphs #2 and #3.

Legeisc
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Member
Legeisc
3 months 3 days ago

On the NPD guys, I wonder if they make better contact than the Yw/OS guys. As it has gotten harder to hit with increasing velocity, maybe the NPD guys are just being able to maintain contact skills better than Yw/OS guys maintain power.

No idea if this is correct…just brainstorming.

Twitchy
Member
Twitchy
3 months 3 days ago

That was my initial thought too. The TTO guys lack contact%, at a time when strikeouts are only going up. Meanwhile the no plate discipline guys might have better contact skills which is why they’re fine. So it’s probably more about ability to make contact than anything else. But the guys with plate discipline + contact would survive the longest.

alekhine8
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alekhine8
3 months 3 days ago

Is >20% a true barometer for “No Plate Discipline” anymore? It seems like that would need to be closer to 25% in the current environment.

Bip
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Member
Bip
3 months 3 days ago

In combination with the low walk rate, I think it works. It means below average walk rate and no lower than an average K rate.

Mike NMN
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Mike NMN
3 months 3 days ago

Perhaps the Young Old guys are losing altitude because of the increasing number of ultra-high velocity arms. If your approach to hitting is to take it deep into the count, and you have lost just a smidgen of reflexes, maybe you fail more often to make good contact.

teakayfortoowon
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teakayfortoowon
3 months 3 days ago

Would showing the percentage of all plate appearances taken by each type of player at each age group help indicate how many are still in the league? It would put the survivor bias into perspective.

bartelsjason
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bartelsjason
3 months 3 days ago

If this was starting since 2005…then, I am guessing the 3TO guys had good bat speed with their power. However, pitchers are throwing harder now, especially relievers, with also more shifting going on since then. 3TO guys have been facing more specialized relievers more often I would assume, and at a time when there bat speed is declining, along with possible slight hand eye coordination.

I would think with the ball being thrown harder and their bat being swung slower, that would be enough to make explain most of the decline.

SomaDaydream
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SomaDaydream
3 months 3 days ago

I’ve been thinking about aging curves lately as well, and how it may relate to pitchers throwing harder than ever. I’d be interested in seeing how players are performing against pitches of different velocities, and if the increasing velocity of pitches is causing an “acceleration” of aging.

Seems like a project for an afternoon or so.

rlwhite
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rlwhite
3 months 3 days ago

“Maybe it’s a quirk of how we measure defense, since this time frame includes the birth of Ultimate Zone Rating in 2002.”

Couldn’t we recalculate without UZR and see how the numbers are affected?

eddo
Member
eddo
3 months 3 days ago

The survivor bias is pretty brutal. This analysis is a valiant effort, but I think the survivor bias makes meaningful interpretation of these curves almost impossible.

Survivor bias is an extremely difficult challenge to overcome in aging analyses. I suppose one way of getting around it might be to include in your player categories only players who reached a certain age in MLB. That would probably introduce a whole question of selection biases, but it would address the survivor issue in some way.

Dominikk85
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Dominikk85
3 months 3 days ago

I’m not sure if there is any signal at all in those data but could TTO sluggers be hurt by a change in pitchers approach, I.e. Pitchers pounding them down the pipe rather than nibbling?

Old sluggers used to still be feared but maybe pitchers now realize that they are not good anymore so they avoid the walk but still give up limited home runs and get many strikeouts with good stuff in the zone.

Pitchers now have less fear and they are drilled to pump strikes early in the count and only nibble if they are ahead.

Paul22
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Paul22
3 months 3 days ago

I think today, especially since pitch f/x was introduced in 2007, the plate discipline guys have been hurt by the expanding strike zone. They take balls that are called strikes (which used to be called balls just the season before), which puts them at a disadvantage behind in the count. The undisciplined guys are relatively unaffected, at least compared to the plate discipline guy, since they just swing at what they want to without regard to the strike zone. They cheat (crowd the plate, back off, etc) and guess (pitch and/or location), and even if the ball is 2 inches off the plate, if that’s what they were looking for, they can hit it.

Antonio Bananas
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Member
Antonio Bananas
3 months 3 days ago

What’s the average career length for each type? It’s not going to show peak, but career length is a decent barometer of long term ability. If one age group has an average career 3 years longer, then that probably means something.

Johnston
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Member
Johnston
3 months 3 days ago

“It’s possible that certain substances were helping the three-true-outcome sluggers stay on the field longer in order to take advantage of their power and patience advantage for a longer period of time. Now that they don’t have those substances, the more naturally athletic players are aging better.”

DING DING DING DING! We have a winner!

Now that players can’t juice with impunity, they are aging normally.

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