Starter Injury Accumulation Leads To Accelerated Aging

In the final part of my latest injury investigation, I trying to see if pitchers who have accumulated a certain amount of injuries age worse than those who have stayed healthy. And if so, are there any rules-of-thumb that can be used. I’ve already examined chronically injured hitters and if accumulated days missed for pitchers lead to more Injured List (IL) trips. The results aren’t groundbreaking findings that constantly hurt pitchers declining faster at certain thresholds but now some numbers can be added to the narratives.

My overall goal is to see the accumulative effect of various injuries can lead to a pitcher aging faster. The factors I had never accounted for are accumulated IL days and times of the IL for elbow, shoulder, or arm injury. Also, I’m only diving into starters (GS/G >= .5) from 2010 to 2018 because relievers, especially closers, are already tough to project. I divided the starters by their age based on a steep production decline starting at age 29. For the pitcher’s talent level, I used ERA- that increase, like ERA, as a pitcher performs worse. The results were a little mixed.

One item to keep in mind, pitchers have historically, maintained their production, or declined as they age. While there is always the exception of a pitcher improving, most are headed down with the average change of 2.8 points of ERA- a year.

The Difference in Production Based on Total Accumulated IL Days
Total IL days Median ERA- Diff Median IP Diff Avg IL Days
28 and Younger
0 1.9 18.1 20.2
1 to 90 2.2 -18.8 29.9
91 to 180 7.3 5.7 37.6
181 to 270 5.1 13.4 35.9
>270 0.6 58.0 38.3
29 and Older
0 0.6 -24.2 15.5
1 to 90 2.9 -17.2 25.8
91 to 180 0.4 -13.0 27.4
181 to 270 5.7 -23.6 39.8
>270 4.5 -4.1 40.4

What I found from this data run and others not listed, age doesn’t matter. Also, while the average IL days steadily climb, the ERA- value jump seems to increase except when it doesn’t. I simplified the results and settled on a 120-day threshold with the following results.

The Difference in Production Based on Total Accumulated IL Days
Career IL Days Median ERA- Diff Median IP Diff Avg IL Days IL Chance
<= 120 days 1.8 -10.5 24.0 40.0%
> 120 IL days 5.2 -8.0 37.8 54.8%

Once a pitcher goes over the 120-day threshold (i.e. a full MLB season), their career declines at a faster than expected rate. Again, there are always going to expectations but rostering too many of these hurt starters increases the downside potential.

Now for one more angle that I had jotted in my to-do book. Most major pitcher injuries center around the arm, so I decided to focus just on them. I bucketed the information by the number of times a pitcher was on the IL for a general arm (e.g. forearm), elbow, or shoulder injury (no wrist or hand). With more than 99% of all instances in the single digits, a simple workable division was easy to find at 2 IL stints.

The Difference in Production Based on Arm-Related IL Trips
IL Stints for Arm ERA- Change Total IL Days IL Days IL Chances
Two or Fewer 2.3 252.6 26.5 42.0%
Three or More 5.5 358.0 39.6 59.0%

Even pitchers who had two or few IL stints weren’t in great shape with them averaging over 200 days on the IL. That third arm related IL trip can be a deal-breaker because the pitcher will, on average, will see their skill degrade about twice as fast as those with two or fewer trips.

And finally here are the pitchers who have over 120 days on the IL and three or more arm related IL stints (min 10 IP last season).

Starters Who Should Age Faster Than Expected
Name Age Days Arm IL Stints FBv
Brett Anderson 32 918 6 90.8
Clay Buchholz 35 717 4 89.5
Rich Hill 40 667 6 90.3
Jason Vargas 37 657 3 84.3
Homer Bailey 34 626 8 93.0
Adam Wainwright 38 618 4 89.9
Hyun-Jin Ryu 류현진 33 558 4 90.6
Charlie Morton 36 551 4 94.4
Michael Pineda 31 511 5 92.6
Yu Darvish 33 492 5 94.2
Nathan Eovaldi 30 470 5 97.5
Zack Wheeler 30 460 5 96.7
Matt Harvey 31 433 4 93.2
Carlos Carrasco 33 432 5 93.5
Anibal Sanchez 36 427 5 90.5
Stephen Strasburg 31 421 6 93.9
Andrew Heaney 29 419 4 92.5
Danny Duffy 31 414 7 92.4
Mike Minor 32 397 3 92.6
Martin Perez 29 377 5 94.1
Andrew Cashner 33 375 4 93.9
Drew Smyly 31 355 3 91.2
Felix Hernandez 34 313 4 89.6
Jhoulys Chacin 32 300 3 90.0
Ivan Nova 33 299 4 92.4
Jordan Zimmermann 34 289 3 90.5
Steven Matz 29 244 5 93.4
Clayton Kershaw 32 217 3 90.4
David Price 34 199 4 92.0
Cole Hamels 36 182 4 91.4
Vince Velasquez 28 144 4 94.1
Gerrit Cole 29 143 4 97.2
Jake Arrieta 34 140 3 92.5
Chris Sale 31 121 4 93.2

Several high ADP names fill the list like Morton, Darvish, Strasburg, Kershaw, and Cole. Does this information mean I won’t roster the pitcher? Maybe. With a fantasy team only starting nine pitchers, I’d like those pitchers to be as rock-solid as possible with little chance of decline. The downside means that I will need them to come with a discount and is an easy tiebreaker. That’s not helpful since that’s everyone’s injury take.

My stance on the information is wishy-washy because I am unsure. I haven’t fathomed a way to weight the information especially if I want to use it to create auction prices. I need to find a way to change ERA- to fantasy-relevant stats. It wouldn’t be that hard but I’m looking at two different inputs (total days and arm related trips). Also, I should incorporate possible time missed from previous IL trips. I’m going to let the information stew for a bit and unless I come to some divine revelation, I’ll perform a forced dive once this season is over or canceled.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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3 years ago

I, for one, appreciate the honesty…”My stance on the information is wishy-washy because I am unsure.”

Great stuff as always, thanks for compiling it.