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Corbin Young examines several fantasy baseball pitcher risers and sleepers displaying changes in their pitch mix, movement, and velocity heading into Week 9 (2025).
Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 9 of the 2025 fantasy baseball season. We researched 24 starting pitchers so far, with three more in this column, two of which flashed ace-like skills and outcomes in 2024. Today's article will discuss a few starting pitchers who made actionable adjustments, like a release point change or a new pitch, location changes, and whether they 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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Spencer Schwellenbach Changed His Righty Approach
Schwellenbach has been throwing more sinkers against right-handed hitters. He traded more sinkers (18.9 percent) for fewer cutters (10.1 percent). Schwellenbach uses the sinker as his third-most-used pitch against right-handed hitters, allowing a .283 wOBA (.308 xwOBA). For context, Schwellenbach's sinker allowed a .409 wOBA (.369 xwOBA) against righties in 2024.
The sinker's movement profile hasn't changed much, so we might speculate on the locations. Interestingly, Schwellenbach raised his arm angle by three degrees by maintaining his vertical release and bringing the horizontal release point 2.5 inches closer to his midline.
Schwellenbach's sinker is more on the inside of the plate toward right-handed hitters, with somewhat more thrown higher in the zone. That's likely an attempt to generate weak contact against the sinker, aligning with the results and groundball rates in 2025. Schwellenbach's sinker has generated more groundballs (76.2 percent), around 13 percentage points higher than in 2024.
Where Have the Splitter Whiffs Gone?
Schwellenbach's splitter elicited a whopping 24.8 percent swinging strike rate in 2024, but it fell to 17.5 percent in 2025. The splitter's movement profile hasn't shifted from the 2024 version. Meanwhile, Schwellenbach's splitter results against left-handed hitters remained similar, with a .141 wOBA (.259 xwOBA) in 2025 versus a .195 wOBA (.231 xwOBA) in 2024.
Like the sinker, Schwellenbach brought his horizontal release point closer to his midline by nearly five inches (4.7), leading to a higher arm angle of almost three degrees. All his pitches have seen a horizontal release point, causing an overall arm angle change in 2025.
The different horizontal release points haven't impacted the movement profiles, but seem to affect the pitch locations. Schwellenbach spotted his splitter down and away from left-handed hitters in the lower right corner of the zone.
When Schwellenbach located the splitter there, it was deadly, evidenced by a .160 wOBA in 2024. The batted ball results have been relatively similar in 2025, so the whiffs could return to the elite levels from 2024. However, hitters have been able to make more contact against the splitter (68.2 percent) in 2025 versus 2024 (55.2 percent). That could be related to Schwellenbach's splitter locations being more volatile.
Summary
Most of the main skills we examine look solid before diving into the pitch-level data and arsenal. Schwellenbach's SwK is nearly identical and above-average at 13.6 percent in 2025. His strikeout minus walk rate fell by five points, but we expect it to be similar to 2024, with similar swinging strike rates. However, it makes us wonder if he adjusts his arm angle and horizontal release point closer to 2024 to see if that impacts the whiffs and locations.
Will Warren's Improved Sweeper Movement
Warren's sweeper has been better in 2025, with more downward movement (three inches) and sweep (four inches). That led to his sweeper having above-average vertical and horizontal movement. The results have improved against right-handed hitters, evidenced by the sweeper allowing a .172 wOBA (.239 xwOBA) in 2025 versus .505 wOBA (.347 xwOBA) in 2024.
Unfortunately, Warren's sweeper hasn't generated more whiffs with an 11.2 percent swinging strike rate. However, his sweeper elicits a better swinging strike rate (18.3 percent) against right-handed hitters. Warren's sweeper lack of whiffs seems to be related to the locations.
Warren has been throwing the sweeper in the zone 47.1 percent of the time in 2025, up from 30.3 percent in 2024. For context, Warren threw his sweeper in Zone 14, which is down and away from righties, 50 percent of the time in 2024. Meanwhile, Warren's sweeper locations fell to 35.1 percent in Zone 14 (low and away from RHH).
Though it's a small change, hitters hardly chased against Warren's sweeper in 2024 with a lower zone rate, so that might be a moot point. Sweepers typically perform well against same-handed hitters, which has been the case with Warren in 2025. However, left-handed hitters have been destroying his sweeper in 2025 (.600 wOBA, .437 xwOBA) versus 2024 (.172 wOBA, .248 xwOBA).
Warren's four-seam results improved in 2025 (.236 wOBA, .306 xwOBA) against lefties, with the changeup outcomes regressing favorably. His best pitch against lefties involves his new curveball, which he throws 9.8 percent of the time versus lefties.
Warren's New Curveball
Since Warren uses a lower arm angle, most of his pitches tend to move horizontally. That means Warren's arsenal lacks depth beyond the sweeper and changeup, to some extent. Warren's new curveball has tons of downward movement, with 13-14 inches of glove side sweep, making it an above-average pitch.
In the early 2025 sample, Warren's curveball leads his arsenal in swinging strike rate at 20.4 percent, though it's a low usage rate, mainly against left-handed hitters. Warren's curveball allows a .177 wOBA (.150 xwOBA) versus lefties. The locations have been pristine, as a backdoor curveball offering against opposite-handed hitters.
He can throw it backdoor and have it low and inside toward left-handed hitters. Warren's curveball has been effective low and inside to left-handed hitters. It could be a situation where hitters expect Warren's noteworthy sweeper, but it's the curveball, leading to hitters swinging over it.
Summary
Warren's xERA (3.65) is one-half run below his actual ERA, telling us to buy into these skills. The skills have been similar in strikeout minus walk (18-20 percent) and swinging strike rate (9-10 percent). He was a breakout pick because of the sweeper, though the changeup hasn't taken a step forward like we hoped. However, Warren's sweeper movement profile hints at more whiffs coming soon, which seems to pair well with the new curveball. Warren made some actionable changes in his arsenal in 2025, so we should notice.
Shota Imanaga's Arm Angle Change
Imanaga lowered his arm angle by three degrees in 2025. That's most notable with the four-seam, sweeper, and splitter dipping by two degrees. Some pitchers have varying arm angles with different pitches, and their arm slot can fluctuate slightly.
We've seen it rise and lower throughout the monthly rolling graphs, and interestingly, there haven't been more than 1-2 inch differences in the horizontal or vertical release points. That's noteworthy because we might speculate on hitters knowing what's coming since Imanaga's overall swinging strike rate fell by three percentage points to 12.7 percent (2025).
Imanaga's Splitter is Losing Whiffs, But Why?
Imanaga's splitter had the biggest decline, with a 26.2 percent SwK in 2024, down to 16.9 percent in 2025. His splitter added three inches of arm-side fade in 2025 while maintaining the downward movement.
That helps the splitter limit the damage, with a .222 wOBA (.307 xwOBA) versus right-handed hitters, though the whiffs haven't been as high. When a pitch generates fewer whiffs and results change, it's fair to speculate on the locations. Imanaga has been throwing the splitters in the zone more often in 2025 (44.7 percent), over four percentage points higher than in 2024 (40.3 percent).
Unsurprisingly, right-handed hitters haven't been chasing as often (41.3 percent) in 2025 versus in 2024 (47 percent) since the splitter zone rates increased. Over 52 percent of Imanaga's splitters were below the zone under the corners in 2024.
That fell to 45 percent in those zones in 2025, with the most significant zone percentage change from the area low and away from left-handed hitters. Besides the locations, hitters seem to be laying off the splitter more often, leading to fewer whiffs, especially since they know it's a tough pitch to square up.
Sometimes the splitter command can be volatile, and Imanaga might be working through some fixes for the locations.
Summary
The luck factors have been in Imanaga's favor again in 2025, with a 4.86 xERA, around two runs higher than his actual ERA. Imanaga has two solid pitches in the sweeper and splitter for whiffs, and the splitter locations look somewhat fixable. The slightly more concerning issue involves Imanaga's arm angle changes and differences between pitches, possibly allowing hitters to guess at the four-seam, splitter, or sweeper. If Imanaga's overall SwK and splitter whiff rates bounce back to 2024 numbers, we shouldn't be that worried.
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