Starting Pitcher Arsenal Changes - Pitch Mix Analysis for Fantasy Baseball (Week 14)

Corbin's starting pitcher fantasy baseball sleepers, breakouts and risers for Week 14 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 14 of the 2025 fantasy baseball season. We researched 30 starting pitchers, with three more in this column, including one veteran and two young arms with small samples. 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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Luis Castillo is Throwing More Four-Seamers to Lefties

Castillo threw his four-seamer around 47 percent of the time in 2023 and 2024 to left-handed hitters. He has been throwing four-seamers more in 2025 to lefties at 50.4 percent of the time. That's notable because Castillo's four-seam usage against left-handers is a career-high.

His four-seamer has been mediocre against left-handed hitters. That's evident by Castillo's four-seam allowing a .351 wOBA (.354 xwOBA) to lefties, similar to recent seasons. We'll examine why the results haven't been as good with the increased usage later. However, that may be an indication that Castillo needs to fade to find success.

Castillo's four-seam has been losing whiffs. His four-seamer elicited a 15-16 percent swinging strike rate in 2022 and 2023. However, Castillo's four-seam whiffs declined to 12-13 percent over the past two seasons.

Castillo's four-seam has lost around an inch of induced vertical break. However, he isn't known for having his heater with tons of vertical movement. Meanwhile, Castillo's four-seam gained around 1-1.5 inches of arm-side fade. That's typically what we expect from Castillo's pitches since he uses a lower 15-degree arm angle.

The Mariners tend to like fastballs in the upper third of the zone. That's mainly where Castillo threw his four-seamers toward left-handed hitters in 2025 and recent seasons. It could be something where the Mariners were attempting to have Castillo generate flyballs (58 percent) via his four-seamer in Seattle's pitcher-friendly home ballpark.

We notice Castillo's four-seam thrown in the upper third tends to generate weak contact. Meanwhile, Castillo's four-seam has been his best pitch to right-handed hitters, allowing a .201 wOBA (.278 xwOBA). That's likely because Castillo's four-seam runs into the hands of right-handed hitters, making it tough to square up. However, Castillo's sliders and sinkers were better against right-handed hitters in 2024.

Castillo's Slider and Changeup Have Been Dropping More

Castillo's slider has been dropping over two inches more, with the changeup adding an inch of drop in 2025. He throws a gyro-like slider, so it hardly generates any horizontal movement. Theoretically, Castillo's slider and changeup, adding downward movement, should lead toward whiffs.

Unfortunately, that hasn't been the case for Castillo. His changeup elicits a 12.1 percent swinging strike rate with the slider at 13.6 percent in 2025. Both pitches lost about 1.5-2 percentage points of their swinging strike rates from 2024. Hitters need to swing to generate swinging strikes.

Interestingly, hitters have not swung against Castillo's changeup, swinging 47.3 percent of the time. For contact, hitters typically swung around 54-55 percent of the time versus the changeup over the previous three seasons. We've also seen Castillo throw the changeup less often in the zone, potentially leading hitters to lay off when it's a borderline pitch.

There has been a similar trend with Castillo's slider, where he lowered the zone rate. Against, opposing hitters might be laying off Castillo's slider, leading to fewer swings and whiffs. One would expect that if Castillo hung his slider, hitters would crush it. We're seeing those trends in 2025.

When Castillo threw his slider in the zone, specifically to left-handed hitters, it allowed a .483 wOBA in 2025, compared to a .367 wOBA (2024) and .442 wOBA (2023). As one would expect, Castillo's slider allows a .116 wOBA (.128 xwOBA) when thrown outside the zone in 2025, aligning with 2024 (.257 wOBA, .155 xwOBA).

Summary

Castillo's xERA (4.36) sits nearly one run above his actual ERA (3.69). He has been fortunate, especially considering his swinging strike rate continued to fall to 11.7 percent, a career low. Castillo still boasts an above-average swinging-strike rate, though we're used to seeing his slider and changeup be nasty.

It's partly about the location and command of those two non-fastballs. Let's see if he makes those minor tweaks in the second half.

Emmet Sheehan's New Changeup

The Dodgers optioned Sheehan after making his shortened four-inning outing, partly to add bullpen depth and slowly work Shohei Ohtani back into the mix. However, let's touch on Sheehan's new changeup because it was significantly different. Sheehan typically consolidated four-seamers and sliders or four-seamers and changeups against right- and left-handed hitters in 2023.

However, Sheehan mixed in three pitches thrown over 15 percent of the time to both sides of the plate in his 2025 debut outing. It was one start, but Sheehan's changeup added 2.5 mph of velocity on Wednesday, leading to the pitch dropping one inch more and losing four inches of arm-side fade.

Interestingly, Sheehan threw a harder changeup, but it lost over 850 RPM in the spin rate on Wednesday. That likely indicates a potential grip change and adjustment. Sheehan's changeup was nasty as a prospect. In Sheehan's brief MLB career, his changeup has elicited a 22 percent swinging-strike rate.

Sheehan's Release Point Change

Sheehan's release points changed in the minor leagues when he threw his changeup in 2025. He raised his vertical release point by over three inches, with a nearly five-inch (4.7) difference in his horizontal release point moving closer to his midline.

The visual below shows Sheehan's MiLB data from 2023 and 2025.

In the one-start sample in 2025, Sheehan's horizontal release point moved closer, like in the minor leagues, with a raised vertical release. That led to a higher arm angle, coinciding with his four-seamer which added two inches of IVB.

It could translate into a better version of Chris Paddack if Sheehan's four-seam maintains the above-average IVB and the new changeup cooks. The wildcard in Sheehan's arsenal involves the slider, but we need more data overall.

Summary

We joked about fading all Dodgers' starting pitchers besides Dustin May in my bold predictions piece. The Dodgers' rotation had tons of money invested on the injured list in 2024. Yoshinobu Yamamoto shoved it in our face, May remained healthy so far, and we've seen their entire starting rotation be overturned.

Fantasy managers should stash Sheehan in an N/A spot in Yahoo leagues, especially if their squad needs pitching help. If Sheehan's release point and pitch movement profiles take a step forward like we saw in the minors and his debut, he could have a breakout season. However, there will be bumps for Sheehan after having Tommy John surgery.

Janson Junk's Different Release Points

The Marlins have used Junk as a bulk reliever in 2025 for five straight outings before facing the Braves and throwing five innings, allowing one earned run, zero walks, and five punchouts. Junk has been gradually lowering his vertical release point, with the most significant change coming from his horizontal release.

Junk's horizontal release point dropped nearly four inches (3.7) in 2025 compared to 2024. For context, Junk's horizontal release point moved closer toward his midline by over one foot (13.8 inches) when comparing the 2025 numbers to his debut season (2021). It could be something fluky, or it might be related to how Junk feels most comfortable bringing his arm angle to be relatively high, but closer to his midline.

How do Junk's release points impact his arsenal? Let's examine the pitch usage in 2025.

Junk Traded Fewer Four-Seamers For More Sliders and Sweepers

With the Marlins, Junk has been throwing fewer four-seamers against right-handed hitters. That's evident in Junk throwing his heater 34.5 percent of the time in favor of more sliders (33 percent) and sweepers (29.1 percent) versus righties. For context, Junk threw his four-seam at 46.2 percent of the time, with the slider thrown at 24.5 percent and the sweeper being hardly used (8.5 percent) versus right-handed hitters.

Junk's slider (.185 wOBA, .319 xwOBA) and sweeper (.187 wOBA, .227 xwOBA) have been two of his best pitches. However, Junk's xwOBA via the slider hints at regression. Meanwhile, Junk's four-seam results improved against right-handed hitters, coinciding with the lower usage in 2025.

Junk's four-seam has been generating high-end levels of IVB (18.5 inches), similar to recent seasons. That should suggest Junk should locate his four-seam in the upper third of the zone. Junk's sweeper movement profile hasn't shifted much. However, Junk's slider has been dropping more (around two inches) while being a slight variation of a gyro-like slider.

Junk's slider (.190 wOBA, .319 xwOBA) and curveball (.197 wOBA, .310 xwOBA) have been two of his best pitches against opposite-handed hitters in 2025. However, be cautious with Junk's expected metrics from the slider and curve, especially since they haven't been generating high-end whiff numbers.

Summary

Junk hasn't been used consistently as a starting pitcher, though Junk flashed quality per-inning metrics in 2025. He showed the best WHIP of his career, mainly via a lower hit rate (seven points below his career average) and a significant improvement in his control (28 percent) in 2025 versus 31 percent in his career. Better control and more whiffs from Junk make him an intriguing pitcher option for most formats.

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