Starting Pitcher Arsenal Changes - Pitch Mix Analysis for Fantasy Baseball (Week 15)

Corbin's starting pitcher fantasy baseball sleepers, breakouts, and risers for Week 15 of 2025 displaying changes in their pitch mix, movement, and velocity.

Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 15 of the 2025 fantasy baseball season. We researched 33 starting pitchers, with three more in this column, including one veteran, a former top prospect, and a post-hype sleeper. Today's article will discuss a few starting pitchers who made actionable adjustments, such as a release point change or a new pitch, as well as location changes, and whether these adjustments will matter moving forward.

For those new to this column, we cover a few starting pitchers and their arsenal changes via pitch mix, velocity, and movement each week. Since it's early, we're looking for new pitches, velocity, and movement changes. When we find significant release point shifts, it can potentially impact their movement profiles in 2025.

Pitchers can make notable changes in smaller samples, so let's see if we can find something with these starting pitchers. Statcast provides so much data to digest and compare quickly to past seasons. Let's look through my process of examining starting pitchers and their arsenals. Reach out to me on X if you have a pitcher and have questions about it. Thank you for reading!

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Shane Baz's New Cutter

Baz introduced a cutter on June 15, throwing them 17.9 percent of the time. He gradually increased his cutter usage to 38.1 percent and 40.2 percent over his past two outings before July 1 (17.8 percent). Baz threw more cutters in favor of fewer four-seamers in 2025.

That's notable because Baz's four-seam hasn't been great, with a .356 wOBA (.364 xwOBA) in 2025, worse than his 2024 results (.321 wOBA, .315 xwOBA). Baz has been mixing in cutters against right-handed (7 percent) and left-handed (7.9 percent) hitters. In the small sample, it's been his best offering in 2025.

Against left-handed hitters, Baz has been generating whiffs (20.8 percent swinging strike rate) and weak contact (.161 wOBA, .166 xwOBA). He tends to locate the cutter down and inside for left-handed hitters, as indicated by the heatmaps. When Baz locates it lower and inside for left-handed hitters, it hasn't generated a hit.

Based on Baz's cutter movement profile, it appears to be an even harder-throwing version of his gyro-like slider. The cutter moves 3-4 inches toward his glove side like the cutter, but the cut fastball doesn't drop as much.

Meanwhile, Baz either locates his cutter low and away from right-handed hitters or high and outside the zone. That's likely an attempt to garner chases and weak contact by keeping it toward the outside portion of the plate or just beyond the zone.

Baz's cutter locations seem somewhat optimal, and it's been a positive pitch addition in the early 2025 sample. He might be throwing his slider too often in the zone, leading to a 52.4 percent zone percentage against right-handed hitters. Unfortunately, right-handed hitters have been destroying the slider, evidenced by a .664 wOBA (.577 xwOBA). It's likely location-related.

When Baz throws his slider in the zone in 2025, it results in a .708 wOBA (.638 xwOBA) against right-handed hitters. That's much worse than his results in 2024, with the slider allowing a .267 wOBA (.288 xwOBA) when thrown in the zone.

Baz's Curveball is Losing Drop

Baz's curveball has been losing 1-2 inches of drop in 2025 compared to the previous two seasons. He has been throwing the curveball 1-2 mph harder, which typically translates to a decline in downward movement. Since Baz's curveball lost downward movement, the whiffs disappeared.

That's evident in Baz's curveball eliciting a 12.8 percent swinging strike rate (SwK) in 2025, down from 15 percent (2024) and 17.2 percent (2022). Baz throws his curveball second-most to right-handed hitters (35.1 percent), allowing a .221 wOBA (.273 xwOBA). Besides the cutter, Baz's curveball performs the best against righties. That's not far from his outcomes in 2024 via the curveball (.218 wOBA, .214 xwOBA).

We've seen a slight fluctuation in his horizontal release point, with it moving 1.5-2 inches closer to his midline. That coincides with Baz losing over two inches of extension, possibly hinting at grip changes, or it's a fluky difference in 2025.

Summary

Baz remains a pitcher who teases us with exciting performances but shows us sobering moments where the ratios look scary. Health has been an issue for Baz, but he has already reached a career-best in innings in 2025. He has a decent 3.67 xERA, which has been better than his actual results.

However, an 11.5 percent swinging strike rate doesn't typically inspire confidence, especially when the control is mediocre with a 35 percent ball rate. If Baz can maintain the success with the new cutter and potentially gain back the whiffs from the curveball, we'll have a more complete pitcher.

Clayton Kershaw Using More Sliders, But Why?

It's 2025, and Kershaw remains a consistent part of the Dodgers rotation after multiple injuries to their starters. Kershaw has been relying on his slider as his most-used pitch throughout the past few seasons. However, Kershaw's slider effectiveness has been on the decline. That's mainly the case over the past two seasons, with Kershaw's slider allowing a .391 wOBA (.392 xwOBA) against right-handed hitters in 2025.

For context, Kershaw's slider allowed a .366 wOBA (.330 xwOBA) in 2024, with the 2023 (.267 wOBA, .285 xwOBA) and 2022 (.246 wOBA, .233 xwOBA) being significantly better against right-handers. So, what changed? Kershaw's slider velocity, vertical, and horizontal movement profiles haven't shifted much over the past few seasons. One would speculate on Kershaw's slider locations.

That's notable because Kershaw has been throwing his slider in the heart of the zone quite often in 2025. Hitters have been whiffing less and posting better contact quality when Kershaw throws the slider in the zone. That's evident in Kershaw's slider, which resulted in a .328 wOBA (.359 xwOBA) and a 12 percent SwK when thrown in the zone in 2025.

Kershaw's slider zone rates increased over the past two seasons, with a 52.5 percent zone rate in 2025 and a 56.4 percent zone rate in 2024. For context, Kershaw threw his slider around 50-51 percent or below over the previous seasons.

When Kershaw throws the slider outside the zone, it typically elicits whiffs. That's evident in Kershaw's slider, generating a 20.2 percent SwK on pitches outside the zone in 2025. However, the contact quality on sliders outside the zone has been the worst of his career, with a .376 wOBA (.311 xwOBA).

Kershaw's Lower Arm Angle

In the Statcast era of recording arm angle (2020-25), Kershaw has been using the lowest arm angle of his career. Overall, Kershaw has thrown from an arm angle of 55 degrees, mainly because his vertical and horizontal release points shifted around one inch from 2024. When we compare 2022 and 2023, Kershaw's release points adjusted closer to two inches in either direction.

With the lower arm angle, he has been posting the most extension of his career. That coincides with Kershaw's four-seam potentially performing well when he locates it in the upper third of the zone. Kershaw's four-seam allows a .298 wOBA, yet the .352 expected wOBA suggests being cautious, especially since it generates zero whiffs. Although Kershaw's four-seam never elicited tons of whiffs against right-handed hitters, opposing teams have been attacking the heater.

We've seen Kershaw's four-seam xwOBA indicate right-handed hitters have been crushing the heater, one of his worst pitches. In the past, Kershaw's four-seam possessed near-elite induced vertical break (IVB), making it hard to square up when it's theoretically rising in the zone.

Like the slider, Kershaw's four-seam has been thrown too often in the heart of the zone. That suggests Kershaw's four-seam locations have contributed to the challenges in 2025. Kershaw has been throwing his four-seam in the heart of the zone 12.6 percent of the time, up from 9.1 percent (2024), yet similar to 2023 (11.3 percent) and 2022 (13.2 percent).

When Kershaw threw his four-seam in the heart of the zone, hitters crushed it, with a .336 wOBA (.361 xwOBA) in 2025. For context, Kershaw's four-seam resulted in a .315 wOBA (.369 xwOBA) in 2024 and a .305 wOBA (.377 xwOBA) in 2023 when thrown in the heart of the zone. We've seen Kershaw often locate his slider low and inside to right-handed hitters, typically leading to quality outcomes.

Summary

Kershaw's xERA over the past two seasons has been the worst of his career, with a 4.10 xERA (2025) and a 4.45 xERA (2024). That suggests Kershaw's skills fell off, meaning he relies more on luck than skill for his outcomes.

For context, Kershaw had a 10-11 percent K-BB rate and a 10 percent SwK in 2024 and 2025 compared to a career K-BB percentage of 21 percent with a 13.8 percent SwK. Be cautious with Kershaw because his best pitch, the slider, lost effectiveness. That's evident by his slider generating a 14-15 percent SwK in 2024 and 2025 versus a career average of 21.8 percent.

A New Horizontal Release Point for Trevor Rogers

Rogers has been using a horizontal release point that's over 5.5 inches closer to his midline. He maintained his high-end extension of 6.6 to 6.7 feet. Besides the slider adding an inch or so of vertical and horizontal movement, his pitch movement profiles haven't shifted much from recent seasons.

That's notable because one would expect pitch movement changes to occur with the horizontal release point shift. However, Rogers' four-seam locations look different in 2025. In 2023 and 2024, Rogers threw his four-seam in the upper third to right-handed hitters around 37-39 percent of the time.

For context, Rogers throws his four-seam 25 percent of the time in the upper parts of the zone in 2025 against right-handed hitters. Based on the heatmaps, Rogers was throwing his four-seamer in the upper third of the zone over the past two seasons. He has been locating the four-seam more in the heart of the zone, yet slightly toward the inside portion of the plate for right-handed hitters.

How is the Four-Seam Better?

Rogers' four-seam has been one of his better offerings against right-handed hitters, allowing a .194 wOBA (.266 xwOBA) in 2025. The results have been the best of his career against right-handed hitters in 2025, with his previous best at a .289 wOBA (.296 xwOBA) in 2023.

Rogers had lowered the four-seam usage against right-handed hitters over the past two seasons after typically throwing it over 45 percent of the time. There could be deception with the four-seamer since it's performing better with a location change.

Theoretically, Rogers' four-seamer and sinker might be tunneling well since he typically generates above-average levels of arm-side movement. That's especially true when we consider that Rogers can "hide" his horizontal release point to be closer to his midline.

It seems like he has been locating the four-seam better, leading to quality outcomes. Since it's rare for pitches to thrive more in the heart of the zone, let's see if Rogers' four-seamer can maintain its success. Admittedly, Rogers used to seem like a stuff-over-command type pitcher, but his Location+ has been better than his Stuff+.

Summary

Rogers has been fortunate by stranding 77 percent of runners and limiting home runs with a 4 percent HR/F in 2025. That's 5-7 percentage points better than his career averages in both categories. The whiffs have been there, with a 12 percent SwK in 2025, though we're dealing with a small sample.

His most notable changes involved the horizontal release point and the locations of the four-seam. If Rogers can find his changeup to generate whiffs like in the past, he could suck us back in if he hasn't already done so.

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