Fantasy Baseball Starting Pitcher Arsenal Changes (Week 22): Pitch Mix, Velocity, and Movement

Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 22 of the 2024 fantasy baseball season. Today's article will discuss Ryne Nelson and Trevor Rogers. For those new to this column, each week, we cover a few starting pitchers and their arsenal changes via pitch mix, velocity, and movement. We're at a point where the pitch movement, arsenal, and velocity should tell us a story with several starts under their belts. With more injuries likely coming soon, we'll want to continue identifying streaming pitcher skills or struggling pitchers with underlying metrics suggesting better results coming soon.

We have about a month left in the fantasy baseball season, causing fantasy managers to make crucial decisions for the final stretch. Pitchers can make notable changes in smaller samples, so let's see if we can find something with these two starting pitchers finding success and understand why. Let's look through my process of examining starting pitchers and their arsenals.

Reach out to me on X if you have a pitcher you have questions about who may be included in a future article.

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Ryne Nelson is Throwing More Four-Seamers

If there's one pitch Ryne Nelson is known for, it's the four-seamer. Nelson's four-seamer possesses above-average induced vertical break (IVB) at 18.2 inches, with 5.8 inches of arm-side movement. From April to June, Nelson threw his four-seamer 48-51 percent of the time. However, Nelson's four-seam usage jumped to 63.1 percent in July and 60.1 percent in August.

The results improved against the four-seam, evidenced by a .268 wOBA in August and .230 wOBA in July compared to a .378 wOBA from April to June. Nelson's four-seam results seem legitimate in the past two months, considering the xwOBA against the four-seam in July (.247) and August (.297).

The visual below shows the rolling swing and miss or whiff rates but still paints the picture of the concerning level of whiffs via all pitches.

When we pair his high-end extension and above-average IVB, one would expect better results and more whiffs via the fastball. However, that isn't the case for Nelson's four-seamer. Nelson's four-seam elicits a nine percent swinging strike rate, leading his arsenal.

When a nine percent swinging strike rate leads the pitch mix in whiffs, it makes us worry about the pitcher sustaining success unless they generate tons of grounders.

Part of the issue with the four-seam seems to be the vertical approach angle (VAA) at -4.8 degrees over the past three seasons (2022-2024). That's in the average range for a four-seam VAA, meaning it's average in flatness.

Hitters perform about the same against Nelson's four-seam when it is and isn't in the upper third of the zone. Nelson's four-seam allows a .319 wOBA (.282 xwOBA) in 2024 with a .323 wOBA (.321 xwOBA) in 2023 when thrown in the upper third.

One strange observation involves Nelson's horizontal release point change over the past two seasons. His horizontal release point moved farther away from the midline of his body by eight inches from 2021 to 2022 and five additional inches from 2022 to 2023. That seems to have caused his four-seam to generate 1-2 more inches of arm-side movement.

Theoretically, having more arm-side run on the four-seam could lead to weaker contact, especially considering if he possibly located it higher inside to right-handed hitters and high and away from lefties. The results against lefties (.284 wOBA) bounced back from 2023 (.384 wOBA), with a similar outcome versus right-handed hitters in 2024 (.344 wOBA) and 2023 (.385 wOBA).

Nelson's Revamped Slider

Nelson's four-seamer has been mixed with above-average IVB, average VAA, and weak results. Meanwhile, Nelson's slider hasn't been much better, with an 8.4 percent swinging strike rate in 2024 compared to a career average of 10.8 percent. He revamped his slider by adding over three mph of velocity compared to 2023.

Unsurprisingly, given the velocity gains, Nelson's slider lost over three inches of downward movement. The breaking ball also lost seven inches of horizontal sweep. While the slider maintained the above-average vertical movement, it went from high-end levels of sweep in 2023 to mediocre in 2024.

It's worth noting that Nelson hardly uses the slider, throwing it 7.7 percent of the time overall and 15.8 percent to right-handed hitters. Among his pitches he throws over 10 percent of the time, his slider performs the best, with a .281 wOBA to righties.

While it's not a drastic difference, it would make sense for Nelson to shift back to his 2023 version since it elicited an 11.7 percent swinging strike rate compared to single digits in 2024.

Nelson located the slider a ton in Zone 14, down and away from right-handed hitters 40.2 percent of the time in 2023, jumping to 51 percent in 2024. They have been effective in Zone 14, with a .225 wOBA in 2023 and .282 wOBA in 2024. It almost seems like his slider in 2024 was a version of his cutter from 2023 since he showed a different cutter in 2024.

Summary

There have been reports of Nelson being removed from the Diamondbacks rotation, with Jordan Montgomery and Eduardo Rodríguez rejoining. However, Nelson has pitched his best in July (2.41 ERA, 3.52 xERA, 17 percent K-BB%) and August (3.38 ERA, 3.19 xERA, 26 percent K-BB%).

There's a good chance that Montgomery and Rodríguez struggle, allowing Nelson to move back into the rotation since he's been thriving.

Though Nelson lacks the whiffs we want to see, he possesses near-elite control, with a 32 percent ball rate. In deep leagues, we may want to hold onto Nelson in case we find quality reliever innings with the chance that the Diamondbacks need him back in the rotation. Overall, Nelson profiles as a control and command-focused pitcher with some intriguing pitch-level metrics.

Trevor Rogers Adjusting the Pitch Mix

Since joining the Orioles, Trevor Rogers has been adjusting the pitch mix. That includes fewer four-seamers, with more changeups and sinkers. Rogers threw the four-seam 28 percent of the time in June, jumping to 40.2 percent in July. However, with the Orioles in August, we've seen the four-seam usage drop to 24.9 percent.

Meanwhile, he bumped up his sinker usage to 27.5 percent in August compared to 19.6 percent in July and 28 percent in June. Rogers gradually increased his changeups from 22.8 percent in June, 21.5 percent in July, and 27.7 percent in August. As one might notice, it's been a mixed bag with Rogers' pitch mix and results.

We've seen the results against Rogers' arsenal shift monthly. The main trend involves his slider and sinker going from awful to better to brutal, plus the four-seamer looking steady over the past two months.

It's an overall small change, but Rogers went from four-seam (43 percent), changeup (25.5 percent), sinker (18.8 percent), and slider (12.7 percent) in 2023 to four-seam (31.6 percent), sinker (24 percent), changeup (23.8 percent), and slider (20.6 percent) in 2024.

The sinker and four-seamer usage change might be Rogers' most notable one in his arsenal because of his sinker's zone rate. Rogers threw his sinker in the zone 56 percent of the time in 2024 and 45.2 percent in 2023. However, it's worth noting the 2024 zone rate via the sinker is similar to his career zone rate at 54.8 percent.

Besides the sinker usage bump, Rogers hardly used it in previous seasons, so take the data with a grain of salt. Rogers' sinker allows a .357 wOBA (.392 xwOBA) when thrown in the zone in 2024 compared to a .074 wOBA (.163 xwOBA) in 2023. Though we have a larger sample of sinkers in the zone in 2024 (291) versus 2023 (36), it seems like something he may want to reconsider.

What's Happening With the Changeup?

The highlight of Rogers' arsenal involved the changeup, evidenced by his career swinging strike rate of 15.7 percent while peaking at 19.4 percent (2021) and 20.2 percent (2023). That suggests some inconsistencies since Rogers' changeup elicited a concerning 12.4 percent swinging strike rate in 2024 and 12.7 percent in 2022.

Interestingly, the changeup's downward movement hasn't shifted much over the past few seasons, hovering around 35-37 inches. The same goes for the horizontal movement, with his changeup possessing 13-14 inches of arm-side fade.

With the similar movement profile on the changeup over the past few seasons, we may hypothesize that the location could be an issue.

Rogers has been throwing his changeup 58 percent of the zone below the zone in Zones 13 and 14 in 2024. However, the changeup has been struggling in Zone 13, which is down and inside to right-handed hitters, evidenced by a .398 wOBA in 2024.

When we compare the changeup usage and results to previous seasons, he threw the pitch in Zones 13 and 14 over 55 percent of the time. The outcomes in those areas, especially in Zone 13, were better, given his .280 wOBA in Zone 13 and .156 wOBA in Zone 14 from 2020-2023.

While the changeup locations and outcomes shifted slightly, there's a chance that hitters have laid off of the pitch when thrown in the zone. Or they're taking a chance and attacking it or being patient when it's close to the lower part of the zone.

When Rogers throws the changeup outside the zone, it translates to a 15.9 percent swinging strike rate in 2024. That's lower than the 2023 swinging strike rate on changeups outside the zone (25.4 percent) but better than 2022 (12.8 percent). However, it's worth noting Rogers posted his second-best swinging strike rate on the changeups outside the zone in 2021 at 23.3 percent.

Summary

Rogers seems to struggle with command of his pitches, making him a volatile starting pitcher with highs and lows. That's evident in his career xERA of 4.31, 12 percent swinging strike rate, and 36.1 percent ball rate. Rogers will continue to destroy the ratios, especially WHIP, meaning be careful when streaming him in all formats.

The movement profiles suggest more whiffs, but Rogers went from an above-average strikeout skill pitcher to below-average (9.1 percent SwK) in 2024. While we want to trust the Orioles' pitching development, it might be a slow burn that takes time, meaning he could warrant more attention in 2025.

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