MGL over at the Book Blog posted this little ditty that has gotten a lot of people thinking about how pitchers age. Here’s the depressing news:
Here are the basic shapes of the aging curves for all pitchers, using the delta method, corrected for survivor bias:
As I said, linear weights against is flat until age 26 (maybe a slight curve upward from 21-23 – it is hard to tell as the sample sizes are small and of course you have large selective sampling for young players that get a second year in MLB) and then a sharp, almost linear curve downward to the tune of around .2 runs a year.
K’s go down a little from 21-23 and then gradually go up until age 29 or so. After that, they drop precipitously – around .2 per game per year.
Walks go down from age 21 to 29, around .08 per game per year. After that, they go up .035 per game per year.
HR per BIP go up from the get go, .055 per game per year.
BABIP goes down slightly from 21-24 and then goes up after that, .005 per year.
MGL’s study starts at age 21, which means it always begins with pitchers who reached the majors at that age. Essentially, the lesson of the study (about which MGL did not go into too much detail, though I’m sure he will eventually) is that, contrary to what most of us would like to believe, pitchers generally do not improve as they age, even when they are young. We’d all like to think that having a young pitcher who is not quite a stud yet could mean that in a year or two he’ll be leading the league in strikeouts, but indeed the vast majority of pitchers “are who they are” beginning at age 21!
Given the caveats of the study (which you can read about in the link), that cannot bode well for the younger Marlins’ starters.
None of us should claim that we expect improvement from Josh Johnson or Ricky Nolasco at this point. Certainly those guys have reached ages at which the improvement would have been minimal and the downside very high. The best you can hope for is that their level of performance sticks as it is and tapers off at a slower rate.
But for the guys who are still “young” in terms of the study (between 21 and 26)? It’s hard to imagine that the best guess is that they would not improve at all. Chris Volstad will be 23 for this season. Sean West will be 24. Andrew Miller and Rick VandenHurk will be 25. Unfortunately for us, our best guess is that they will stay static rather than become better pitchers. In MGL’s overall study, only K% gets better with age, up until apparently age 29. The other effects only go downhill.
Now, this does not preclude that individual pitchers could get better, and neither does it mean that pitchers don’t improve in aspects of their game. I think the traditional opinion of young pitchers “learning to pitch” probably does have an effect, and MGL and other commentors mentioned this as well. It may be that, as a whole, the physical decline of pitchers past 26 outweighs the knowledge/mental aspect of pitching gained at that point.
So which of the four pitchers would we expect to be able to buck this general trend? Based on the comments I’ve read so far, it may be pitchers who are:
1) Young enough to still be able to stave off the physical decline
2) Have more upside in terms of mental aspects of the game
The first category precludes Miller and VandenHurk. Miller seems to be the furthest from being able to develop. Not only is he still lacking in the mental aspect of pitching (his walk rates likely have just as much to do with his “learning to pitch” as they do with his physical control), but he also is among the oldest of these pitchers. By the time he improves enough mentally, he may not be able to offset the effects of aging. Needless to say, if he is who he is now, he will not be a valuable pitcher in the majors. It would seem that these two pitchers would be fighting a losing effort in trying to improve their pitching skills while facing their rapidly increasing physical decline.
The other two starters seem like they could improve yet. Of the four, I would bank on West the most. He was 23 last season and was thrown into the fire and pitched decently. He already came in with a track record for strikeouts and groundouts, two things you definitely want to see. If his K% continues to rise, he could make up for those walks, and if his ground ball tendencies are real, he’ll limit the home run growth. Volstad could show similar development, but scouts never had him as much of a strikeout guy. His meal ticket was always the grounder; if those rates improve, he too could stem the expected home run growth, but if not, K% and BB% are average at best.
Of course, the important thing is that we could never reliably tell. There is so much that goes into pitching that it would be really difficult to apply these general aging curves to any specific pitcher. We know now that Johnson and Nolasco have a better chance of showing improvement and declining more slowly because we know that they are better pitchers (though MGL states that controlling for quality of pitcher yields the same results), but there would be no way for us to guess that five years ago. The suggestions that MGL makes are just the best guess; ultimately the scouts will also have a say on which of these players can still improve.