Baby-faced aces: A trend, or a trifle?

“Good young pitching” was a dominant theme of the 2013 MLB season, as discussed by fans and media. Ever skeptical of perceived trends, I had to ask: Were the numbers truly unusual, or was the discussion based on selective notice? And if the numbers do stand up to initial scrutiny, are they part of a trend, or just a random event? Here’s a quick study of pitchers and age since 1998, the last expansion year.


I went at this two ways. First, I just counted the pitchers meeting certain thresholds of age, innings and WAR output. I’ll show two of those graphs, both suggesting that this year was unusual. Yet this method alone does not indicate a trend. The second method is broader and, I think, much more revealing.

Young standouts

Our first graph covers pitchers age 23 or under as of June 30, a simple count of two groups:

  • those with at least 100 innings that season, and
  • those with 100+ IP and at least 1.0 WAR per 100 IP.

Granted, all such thresholds are arbitrary, and this first pool excludes such 2013 stars as Chris SaleMatt Harvey and Stephen Strasburg (all age 24), along with postseason stars Michael Wacha and Trevor Rosenthal (young enough, but short of 100 IP). But this is just one quick look:

1998-2013 Ps 23-under with 100 IP and 1 WAR per 100


The tally of those with 100 innings (the blue bars) was not unusual: 16 pitchers age 23 or under reached 100 IP in 2013, which is just a bit above average for the period (15.2).

But the WAR-based count (red bars) is extreme, indeed: 14 pitchers age 23 or under had both 100 IP and 1.0 WAR/100 IP. That’s five more than the period average (8.9), and two more than any other year in the period.

(Here are the names for 1998-2013 meeting both criteria, and the detail for 2013. We can’t help but notice that all but one of this year’s group were NLers, and four were Miami Marlins. But let’s stick to the big picture.)

For all ages this year, 79 pitchers met both criteria, so the 14 youngsters comprised 18% of that total. That, too, is the high for the period, whose average is 12%.

The next graph varies the theme, raising the cutoffs to age 25 or under and at least 1.5 WAR per 100 IP. This season had 23 such pitchers, three more than any other year in the period, which averaged 14.7. (In fact, 2013 had the most pitchers ever meeting both criteria, but that comes with a grain of salt: there are simply far more pitchers in the current era than for most of MLB history.)

1998-2013 Ps 25-under with 100 IP and 1-point-5 WAR per 100


(Again, here are the names for 1998-2013, and the detail for 2013.)

This year’s 25-and-unders comprised 43% of all pitchers meeting the IP and WAR criteria, also the high for the period, which averaged 30%.

But while both graphs peak in 2013, neither one shows a clear trend, either for innings alone or for innings-plus-WAR. In both cases, the WAR-based counts for 2012 and 2011 were below the period average. Running more graphs with various cutoffs might bring out a trend … or not. But from what we see here, it’s too soon to say if this year’s numbers are anything but cyclical variation.

Average age

What if we move past arbitrary standards to a broader measure of pitchers’ ages? I graphed the average age figure given by Baseball-Reference (“PitchAge”), which is weighted by games — more precisely, weighted by [3*GS + G + Sv]. I’ll call this figure Games age. That graph was suggestive, but hardly conclusive; the range for 1998-2013 is less than one full year, and this season’s 28.4 is just a bit under the period average of 28.7.

Seeking to gauge not just how much they pitched, but how well, I calculated WAR-weighted averages, by:

  1. multiplying each pitcher’s age by his WAR;
  2. totaling those figures; and
  3. dividing that by the total of pitchers’ ages.

I’ll call this figure WAR age. The last graph shows both of those figures, with Games age in blue, WAR age in red:

1998-2013 Ps Average age WAR age and Games age


Now, that looks like a trend, no? In the latter half of this period, both age measures have been falling pretty steadily, but especially the WAR age. That measure in 1998-2005 was over 29 each year, averaging 29.3. Since 2006, WAR age has been under 29 each year, averaging 28.3. And the 27.9 WAR age for 2013 is the lowest for the period studied.

The range of WAR age for 1998-2013 was from 27.9 to 29.9, with an average of 28.8. The high WAR age for 1998 might be an effect of expansion, bringing in more young pitchers who weren’t very good. But expansion effects tend to be smaller and briefer than is widely believed, and the ’98 expansion, from 28 to 30 teams, added just 7% to the total rosters. Anyway, that spike is gone by 1999; the WAR age holds between 29.1-29.5 through 2005, then starts a steady decline.

I would not assume that a rise of young pitchers is the whole cause of declining WAR age. Recent years have seen fewer star turns by older pitchers. A count of 4-WAR seasons by pitchers age 36 and up shows 31 such seasons in the first half of this period (five each by Randy Johnson and Roger Clemens), but just 11 such seasons in 2006-13. Some of you may have theories for this decline, but I’ll leave it alone.

Lastly, I spot-checked the WAR age for a few seasons outside the period, in four pairs:

None of those eight seasons had a lower WAR age than this year’s 27.9, but 1972-73 and ’78 all hit that same mark. The other five years were between 28.0 and 28.4.

Viewed together, these data tend to suggest that the high WAR age for 1998-2005 (averaging 29.3) was aberrant, at least for the divisional era. The current trend could be just a return to historical norms, or it might be something new altogether. But it does seem to be real — and, in some cases, spectacular.

Your thoughts?

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11 Comments on "Baby-faced aces: A trend, or a trifle?"

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I always like to look at these things through the lens of my Cleveland Indians. And what did I find? Last year, the Indians only gave 130.3 innings to pitchers age 30+ (9.0% of total innings). They received +12.9 WAR from pitchers age 29 and under and -1.0 WAR from pitchers age 30+.

And of the 28 players to take the mound for the Indians last year, the oldest was age 33 Rich Hill.


From the Giants perspective, our youngest pitcher was worth 3.8 WAR and our oldest two pitchers were worth a combined -4.6…

In fairness to Messrs Zito and Vogelsong there was also a lot of rubbish in between.


The Yankee Lens…

671 innings went to age 30+. 46.4% of total.

Ladies and gentleman, the 2013 NY Yankees
WAR leaders for pitchers age 30+…

Hiroki 4.1
AP 2.5
Mo 2.5
CC 0.3 yikes!!!
Matt Daley 0.3 in 6 innings. Double Yikes!!!

I think more teams are realizing that it makes no sense to keep a prospect in the minors when: 1. A hard thrower is never going to throw harder – they might never be better. 2. Years under team control – you’d rather have a season now, when you know your young pitcher is healthy, than later when he might not be. 3. Injuries are going to happen, so you might as well try and get some value out of them beforehand, in case they never recover. 4. Young is cheap, and you can often get a decent/good season out… Read more »

JA when are you gonna get a real job (in someone’s front office)?

no statistician but

Somehow this post reminded me—since I’m a contrarian by nature, I suppose—of the fabulous young pitching staff of the 1937 Boston Bees, led by rookies Jim Turner and Lou Fette. Both won twenty games, a feat that I don’t believe has been matched since. Turner’s WAR was 5.4, Fette’s 3.9. Turner was a mere 33 years of age, and Fette had hardly begun to shave at age 30.

Richard Chester

There have been 34 rookie pitchers with 20+ wins (in the game searchable era). Only 9 of them went on to 100+ lifetime wins. Alexander and Mathewson had the most, 373. Four of them won fewer than 20 games for the remainder of their careers. One of them, Henry Schmidt, pitched just one year in the ML. He lived on the West coast and decided that he did not want to spend 6 months a year away from home.

no statistician but


I meant, of course, two 20-game winning rookies on one team.

Richard Chester

I realized that, I just wanted to toss in more information.

While we’re on the subject I have found one other season of two such rookies on the same team in the same year. In 1912 Buck O’Brien and Hugh Bedient each won 20 games for the Red Sox. And shouldn’t the O in O’Brien belong to Bedient?:-)

Bryan O'Connor
I hate to be the first to inject my least favorite one word narrative, but… steroids. I believe PEDs not only kept some older pitchers healthy and on the field well into their 30s and sometimes 40s, but they fooled GMs into believing the aging curve had been “fixed”. No good pitching talent coming up through the system? No problem. Sign Randy Johnson, Jon Lieber, Kevin Brown, and Javier Vazquez and assume they’ll each give you 200 quality innings, as they always have. In contrast, more GMs today seem to see the value in taking risks on 22-year-olds whose arms… Read more »

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