It’s no secret that generating more strikes will lead to a higher chance of strikeouts, but is there a way to correlate a pitcher’s swinging strike percentage with the final strikeout rate? If we use last year’s qualified pitchers as a guide, then we can see that there is, indeed, a mathematical connection between the two.
This is clearly good news, as we can target pitchers with higher swinging strike percentages as candidates for expected high strikeout rates. The key, however, is in finding pitchers that still have room to grow with the result of strikeouts from the input of swinging strike percentages.
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SPs Due for Regression Based on Swinging-Strike Rates
Below is a chart of strikeout rate per nine innings vs. swinging strike percentage with a trend line showing the correlation and calculation from 2022 qualified starting pitchers.
Among all qualified pitchers, Marco Gonzales had the fifth-lowest swinging strike rate in 2022. Not surprisingly, this resulted in the lowest actual strikeout rate in the league. Gonzales has never been known as a strikeout pitcher, but the distance from his career averages suggest that last year was more of an outlier than anything else.
Gonzales saw a spike in ground-ball rate — which obviously ties into the low swinging strike percentage — but his fastball velocity held for a third consecutive season. His hard-hit percentage also dipped to the lowest point of his career, so the only piece missing in his arsenal is a raise in strikeout rate. While it likely won’t be an extreme jump, there is definitely room for improvement.
On the opposite end of the spectrum from the aforementioned Gonzales are two pitchers that landed in almost identical places. Shane McClanahan and Kevin Gausman finished with swinging strike percentages of exactly 15.5 and, as a result, had strikeout rates of 10.50 and 10.56 per nine innings, respectively.
Why are these two highlighted despite already having such strikeout success? Because they are technically below the expected strikeout rate for their high swinging strike percentage. Using last year’s data to form the trend line, both pitchers should have eclipsed 11 strikeouts per nine innings, which puts them further into the upper echelon of this category.
Perhaps the best news for both pitchers is that their swinging strike rates improved from 2021 to 2022, so there is no reason to expect either to drop off in 2023.
One of the more interesting cases for 2023 is Tyler Anderson. A former member of the Rockies, it’s difficult to take most of his first few years in the league seriously, but he obviously made giant strides in first full season with the Dodgers. He finished with an outstanding ERA of 2.57 and, even if we use his FIP as a means for regression, he still has some room to move without losing all of his value.
The reason why Anderson is highlighted in this column, however, is that his 11.80 swinging strike percentage should have produced a strike rate around one batter per inning — Justin Verlander and Kyle Wright had similar swinging strike rates and each struck out at least 8.5 batters per nine innings.
Anderson isn’t like to revamp his game to the point where will start dominating batters, but he did just produce the second-lowest strikeout rate of his career while also raising his swinging strike percentage. For as much as he might regress in his ERA, there is a chance that is offset by a better strikeout rate.
There’s a bad for every good. For as much as we want to use this article to target pitchers who can improve their strikeout rates, we need to be fair that some will start to decline. Charlie Morton and Aaron Nola, both of whom averaged more than 10.3 strikeouts per nine innings, sat well above the trend line. Most players who had double-digit strikeout rates on a per-nine inning basis also had a swinging strike percentage of at least 14. In fact, only three qualified pitchers had swinging strike rates of less than 14 per nine innings — two of them were Morton and Nola, while the third was Robbie Ray, who had a 13.5 swinging strike percentage and 10.1 strikeout rate per nine innings.
All told, Morton and Nola were outliers, but they also followed the same trend that counters what was written about the prior group. Compared to 2021, both pitchers had slightly lower strikeout rates — per batters faced — and swinging strike percentages in 2022. It’s possible that neither pitcher crumbles in the strikeout category, but, if there is a decline, we now see how it would happen.
For the majority of this article, we have looked at pitchers who have seen a change in their swinging strike rates that could lead to a continuation in the same direction. Pablo Lopez is the rare example of a player who dropped his strikeout rate significantly from the prior two seasons but posted the highest swinging strike percentage of his career.
This makes Lopez unique. He started a full 32 games for the first time in his career, had impressive numbers throughout, but also dropped his fastball velocity to the slowest since his rookie season — 2018. While we could argue that an increase in swinging strike percentage would only raise his strikeout potential, it’s more likely that a pitcher who had hovered right around 12 percent for 2020 and 2021 would see a regression back down to that number — from 12.7 percent in 2022. If that decrease happens, it will likely result in the strikeout percentage dropping, too.
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