Starting Pitcher Arsenal Changes - Pitch Mix Analysis for Fantasy Baseball (Week 13)

Corbin's starting pitcher fantasy baseball sleepers, breakouts and risers for Week 13 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 13 of the 2025 fantasy baseball season. We researched 30 starting pitchers, with three more in this column, including deep league streamers that caught our eye. 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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Emerson Hancock Uses a Lower Arm Angle

The injuries have tested the Mariners' starting rotation depth, including needing to rely on Hancock more often. Hancock has been throwing from a lower arm angle in 2025, dropping by 6 degrees. That's mainly because Hancock's horizontal release moved over seven inches (7.2) farther from his midline.

Hancock's horizontal release point change coincided with fewer inches of extension (3.6). That should change Hancock's pitch movement profiles, especially via the sinker and slider. Hancock's sinker added one inch of arm-side movement in 2025 compared to 2024. Though his sinker generates an above-average amount of horizontal movement, it doesn't induce weak contact.

Hancock's Sinker and Four-Seam

Hancock's sinker is his primary pitch (43.1 percent) thrown to right-handed hitters. His sinker allows a .383 wOBA (.361 xwOBA) to righties in 2025, similar to previous seasons. If Hancock can consistently locate the sinker more toward the inside corner for right-handed hitters, there might be better contact quality outcomes.

Unfortunately, the sinker results against left-handed hitters have been worse in 2025. That's evident by Hancock's sinker allowing a .441 wOBA (.419 xwOBA) to lefties, though his four-seamer serves as his best fastball to opposite-handed hitters. His four-seamer results in a .280 wOBA (.331 xwOBA) to left-handed hitters.

Hancock could benefit from locating his sinkers up higher in the zone or lower in the zone. Typically, we don't see many sinkers higher in the zone, which could confuse hitters. It's something he throws over the middle of the plate, and then it fades toward the outside corner. We noticed Hancock drops his arm angle even further (17.5 degrees) when he throws the sinker, an 8-degree decline from 2024.

That could mean hitters can expect what's coming from Hancock when he drops his arm angle for the sinker. Hancock has been gradually dropping the four-seam usage to left-handed hitters. Meanwhile, he increased the sinker and changeup usage throughout his brief MLB career. One might argue for Hancock to increase his four-seam usage if it remains effective.

Interestingly, Hancock's four-seam locations against left-handed hitters in 2024 look better than in 2025. However, Hancock's four-seam results against left-handed hitters improved slightly in 2025. So, maybe the four-seam outcomes regress.

Hancock's New Slider

Hancock's four-seamer elicited a 12.6 percent swinging strike rate in 2025, with the changeup being the other notable option. His changeup generated a 12-13 percent swinging strike rate in the previous two seasons. Hancock developed a new slider this season, though it hasn't led to many whiffs. His slider elicits a 14.3 percent swinging strike rate. So, what's new about his slider?

Let's start with the vertical movement. Hancock's slider dropped over four inches more in 2025 compared to the 2024 season. The slider added significant downward movement over the past two seasons because he throws it 4-5 mph slower. Since Hancock threw a slower slider, it also added over 200 RPM in the spin rate.

Hancock has been locating his slider down and away from right-handed hitters, throwing it there 42-44 percent of the time. After looking at the slider zone rates, it begs the question of whether Hancock should throw the slider less often in the zone. He currently throws the slider in the zone 43.8 percent of the time.

When Hancock threw his slider out of the zone, it allowed a .089 wOBA (.080 xwOBA). That's better than the slider outcomes outside the zone in 2024, with a .251 wOBA (.282 xwOBA). It's easier said than done, but the locations speak for themselves. When Hancock hangs his slider in the zone against right-handed hitters, they crush it in 2025, with a .460 wOBA (.427 xwOBA). He needs the slider to be effective because it's his only offering that moves toward his glove side.

Summary

Hancock isn't much more than a deep league streamer or more of a real-life asset. His xERA (4.30) has been slightly better than his actual results, but a single-digit K-BB percentage (9 percent) and swinging strike rate (9.2 percent) don't inspire confidence. If a pitcher lacks whiffs, we want them to have high-end control, but that hasn't been the case, either, given Hancock's 36 percent ball rate. Theoretically, Hancock's sinker and four-seam should generate weaker contact, with the slider eliciting more whiffs if he throws it more outside the zone.

Charlie Morton is Throwing More Curveballs Again, and It's Working

Though Morton's overall curveball usage in 2025 is down five percentage points (37 percent), he has been throwing it more each month. Morton threw his curveball in April 34.2 percent of the time, increasing to 38.4 percent (May) and to 41.3 percent (June).

The results have improved, with a .435 wOBA in April, .277 wOBA in May, and .218 wOBA in June. That could be fluky or a concerted effort to trust his best pitch. Given the better contact quality, Morton's curveball elicited more whiffs in June than in April. So, what changed?

Morton's curveball added horizontal movement throughout the 2025 season, leading to it sweeping more often by two inches (17). The curveball's horizontal movement fluctuated throughout his career, with a gradual decline. However, Morton's curveball added two inches of sweep in 2025.

With the additional horizontal movement via the curveball, he has been locating it more consistently. Morton's curveball thrives when he throws it low and away from right-handed hitters (37.8 percent), leading to a .172 wOBA in 2025.

It's typically his best offering against both sides of the plate. That's evident by Morton's curveball, resulting in a .307 wOBA (.288 xwOBA) against righties and a .322 wOBA versus lefties (.319 xwOBA). Morton's curveball can be volatile, so let's see if the changeup can be something notable.

Morton's Changeup is Dropping More

Morton introduced a changeup in 2021 with the Braves. His changeup added 1-2 inches of downward movement in 2025, which theoretically should lead to more whiffs. Unfortunately, Morton's changeup hasn't elicited more whiffs, with a measly 8.8 percent swinging strike rate in 2025, four points below his career average (14.2 percent).

However, Morton's changeup led to improved contact quality against left-handed hitters. Morton's changeup results in a .301 wOBA (.269 xwOBA) versus left-handed hitters in 2025. That's a similar expected wOBA to 2023 after some problems in 2024.

Besides the downward movement, Morton's changeup locations bounced back closer to 2023. Morton has been throwing his changeup in the zone 36.2 percent of the time against left-handed hitters, down from 43.2 percent (2024) and 33.7 percent (2023).

Summary

Morton's xERA (4.26) suggests the results should continue to improve for him with an ERA above 6.00. Morton's overall swinging strike rate has faded to 11.6 percent in 2025 after numbers closer to 12-13 percent in recent years. If the curveball command dips for a while, the results could be ugly. We can stream Morton, but he will destroy your team's WHIP.

Bailey Falter is Throwing More Sinkers to Left-Handed Hitters

Falter is throwing his sinker 27 percent of the time against left-handed hitters in 2025. That's up from 19.6 percent in 2024 and 8.1 percent in 2023. The sinker added one inch of induced vertical break (18.3 inches), pairing closely with the four-seamer (18.9 inches).

Falter's sinker allows decent results against lefties, resulting in a .292 wOBA (.339 xwOBA). It's been his second-best pitch behind his slider (.247 wOBA, .347 xwOBA) versus lefties. Falter's sinker locations in 2025 shifted more toward the inside corner against left-handed hitters.

It was somewhat similar to 2024, but we saw more of his sinker against lefties come higher and inside the zone in 2025. Sinkers thrown higher in the zone can be sneaky, especially since hitters might not be expecting it. Falter's sinker hasn't allowed a home run, but it has generated infield flyballs 47.4 percent of the time.

Falter's sinker hasn't been dominant, but it limits damage. Take note of Falter's sinker location and usage changes against left-handed hitters.

Falter's New Splitter

Falter introduced a splitter into his arsenal in 2023. However, it's a different splitter in 2025. Against right-handed hitters, he threw it 3 percent of the time in 2023, under 1 percent in 2024, then increased the usage to 9.3 percent in 2025. For context, it's Falter's least-used pitch against right-handed hitters, resulting in a .244 wOBA (.378 xwOBA).

The movement profile shifted by adding 2-4 inches of downward movement while losing 1-2 inches of arm-side fade. Besides the slight movement variations, his splitter has a ridiculously low spin rate (928). For context, Falter's splitter spin rate is close to Bryce Miller's (912 RPM) and George Kirby's (946 RPM) split-finger from the 2024 season.

Unfortunately, Falter's splitter has one of the lowest whiff rates among pitchers who threw 50 of them when sorting the leaderboard by pitchers with the lowest splitter spin rate. We hardly see splitters have a low swinging strike rate like Falter's (2.4 percent). Falter's splitter locations are an issue.

That's mainly evident by Falter throwing his splitter in the zone 52.9 percent of the time, similar to his curveball, four-seam, and sinker zone rates. If Falter can throw it lower and below the zone, we could see a slight uptick in whiffs.

Falter likely tweaked his splitter grip to account for the changes in the spin rate. There's a fixable change in the locations, though it's easier said than done, especially with a newer pitch for him.

Summary

Falter's xERA (4.55) sits over one run higher than his actual outcome. For context, Falter's xERA sits around his career norm (4.53), suggesting he continues to outperform his skills. We usually want to tread cautiously when a pitcher has career bests in his hit and strand rates, plus a career low in HR/F (9 percent).

That's especially true when a pitcher lacks whiffs, like Falter's low 7.4 percent swinging strike rate, 1.5 points below his career norm. Falter's sinker locations against lefties and the new splitter have been notable, but not enough to give us confidence in him as more than a streamer.

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