Do Pitchers Struggle as Their Stuff Declines?
Nathan Ray Seebeck-Imagn Images
Earlier this week on the CBS Fantasy Baseball Today podcast, Chris Towers noted that Shane McClanahan was struggling more than he would have expected, even with his STUPH model grades down. Chris wondered if a pitcher’s STUPH drops to a new level, does the pitcher perform worse than those who were already at that level? Pitchers need time to adjust to their new talent level. Well, I decided to give the question a quick look.
When McClanahan last threw back in 2023, he had a Pitching+ of 115, and now has a Pitching+ of 90. While he has the same number of strikeouts (9 K/9), the rest of his results have been horrible (5.00 ERA, 1.33 WHIP) as his walks have ballooned (5.5 BB/9). The biggest issue with analyzing this change is that it is extreme, with a two-year gap between throwing. I needed to simplify the search.
Finding a large enough sample set was a pain. The set needs to include starting pitchers (I stayed away from combining starters and relievers) with a STUPH decline into a range with a large enough sample of other pitchers already pitching in that range. And all this occurs in the few seasons that STUPH models have existed. In the end, I went with Pitching+ as my metric because I wanted the pitcher’s overall talent. Also, I wanted a quick snapshot, not a full-blown study. Future studies could use several factors.
For the sample, I took all starters with at least 40 IP in back-to-back seasons. I subdivided that group into pitchers who saw their Pitching+ drop between five and 10 points into the 95 to 105 Pitching+ range (n=26). Then I created another group of pitchers with a 97.5 to 102.5 Pitching+ range in subsequent seasons (n=37).
Here are the average values from the two samples.
| STUPH Model | Previous Pitching + | Pitching+ | Stuff+ | Location+ | IP | ERA | FIP | xFIP | SIERA | K/9 | BB/9 | WHIP |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pitching+ Decline to Range | 106.8 | 100.2 | 96.7 | 102.8 | 108 | 4.50 | 4.51 | 4.26 | 4.34 | 8.70 | 3.39 | 1.35 |
| Pitching + Stable in Range | 100.0 | 100.1 | 97.5 | 102.1 | 125 | 3.86 | 3.97 | 4.07 | 4.15 | 8.45 | 2.84 | 1.24 |
Even though Pitching+ was the factor controlled for, both sets’ Stuff+ and Location+ values ended up similar. And that’s about it for any similarities. The declining pitchers threw fewer innings (possible injury?) with an ERA that’s 0.64 higher and a WHIP that’s 0.11 higher. These pitchers seemed to struggle at the new talent level compared to pitchers who had time to adjust to it.
The effects seen by this one small subset mean someone should dive in to verify the results. The different ways to cut up the data could be endless. Different change sizes? Include TheBot Values? Do changes in Stuff values lead to changes in Location values? After a season with worse STUPH, do the pitchers’ results improve? As long as the sample sizes remain reasonable, the combinations are endless. I’m afraid Chris opened a can of worms.
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.
Who writes the sub-headlines? Because this one says “Yes, and by quite a bit.”
I didn’t find that in the article at all. Please don’t be AI…
Interesting. To me this suggests when a pitcher pre-injury displays specific results given his STUPH number, you can only reliably assume results if the pitcher post-injury displays the same STUPH. When that declines, to a level that other pitchers demonstrate success, the pitcher needs to essentially re-discover how to pitch but at a lower level. Makes drafting post-injury players when the injury assumes a major impact on STUPH like TJ, TOS, anything with the arm really, a very risky bet
The answer to the question presented seems obvious–yes pitchers struggle with reduced stuff. Some adjust and find a new level but most probably end up worse than before.
That said, it seems premature (admittedly with the benefit of an additional game) to conclude that McClanahan will end up with materially reduced stuff. He had just pitched his first five games after being sidelined for nearly three years. And, as one might expect, the first three games were not so great. He has pitched again, and his second three games look pretty good.
So, I would say this was a nice little confirmation analysis, but we need a bigger sample size before we make any conclusions about McClanahan (or any pitcher coming back from a long layoff).