Fantasy Baseball Starting Pitcher Arsenal Changes (Week 25): Pitch Mix, Velocity, and Movement

Corbin Young examines two fantasy baseball pitcher risers and sleepers displaying changes in their pitch mix, movement, and velocity heading into Week 25 (2024).

Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 25 of the 2024 fantasy baseball season. Today's article will discuss Davis Martin and Yusei Kikuchi. 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 less than 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. This is the final article of this series for the 2024 season. Thank you for reading!

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Davis Martin's Intriguing Changeup

Martin's changeup pops via the movement profile, evidenced by the above-average downward movement. Interestingly, Martin's changeup only elicits an 11.5 percent swinging strike rate. Though Martin had a one-year gap between his MLB data, his changeup added 3 mph of velocity and nearly six inches of downward movement.

The visual below shows the rolling swing and miss or whiff rates, according to Baseball Savant, but it still paints the picture of the underwhelming number of whiffs.

Martin's changeup swinging strike rate nearly doubled in 2024 compared to 2022 (6.2 percent). That doesn't surprise us, considering the added velocity and downward movement, which typically translates to more whiffs.

Against left-handed hitters, Martin's changeup has been his second-best pitch, allowing a .180 wOBA, though the .379 xwOBA suggests some regression. It's worth noting that Martin mixes in five pitches over 13 percent of the time against left-handed hitters. That means he uses multiple pitches and finds success via other solid offerings in the cutter (.273 wOBA, .321 xwOBA), slider (.260 wOBA, .224 xwOBA), and curveball (.160 wOBA, .235 xwOBA).

Part of the changeup issues involves Martin throwing it tons in the zone since it's not eliciting a high whiff rate. The expected stats for Martin's changeup suggest the results should be worse based on the poor contact quality. Martin throws his changeup in the zone 50 percent of the time, over 10 percentage points above the league average of 38.9 percent.

It might benefit Martin to throw his changeup more outside the zone, especially considering the near-elite levels of downward movement. Unsurprisingly, when Martin throws his changeup in the zone, it allows a .304 wOBA (.453 xwOBA). That's worse than his results in 2022 (.353 wOBA, .409 xwOBA), which hints at potential location challenges.

Meanwhile, it generates near-elite results outside the zone, evidenced by a .131 wOBA (.183 xwOBA) and a 20 percent swinging strike rate. However, we're dealing with small samples, so hopefully, he can fix this over time.

Martin Lowered the Slider Usage

We've seen Martin lower the slider usage in 2024, though it's a small sample of two months. Martin threw a slider 45 percent of the time (July), down to 26.7 percent (August), and 14 percent in one September start. That's odd because the slider has been his best pitch for swings and misses, with a 17.9 percent swinging strike rate.

Hitters haven't been chasing the slider as much, around 10 percentage points less often in 2024, while maintaining the zone rates. Though hitters made more contact on the slider in 2024 (66.3 percent) compared to 2022 (59.7 percent), the contact quality results stayed the same. That's evident in his .237 wOBA (.242 xwOBA) in 2024. Martin's slider has been effective against both sides of the plate, evidenced by a .227 wOBA versus righties and a .260 wOBA allowed to lefties.

Since Martin's slider movement profile hasn't changed from 2022 to 2024, it's possibly more related to the location and command. Martin peppers the slider down and away from right-handed hitters 45.1 percent of the time, translating to a .232 wOBA in 2024. The location rate in 2022, down and away to righties (43.9 percent), hasn't changed with high-end results (.168 wOBA).

One might wonder why there was a slight decline in slider usage for Martin, especially considering the positive results. The slider's movement profile doesn't suggest high-end stuff, but it's logical for him to use it slightly more to attack same-handed hitters.

Summary

Martin's control looks like a problem, evidenced by his walk rate. However, Martin has average control, with a 36.6 percent ball rate in 2024 compared to 33.7 percent in 2022. His average control may lead to an unappetizing WHIP, especially if the luck factors aren't in his favor.

Look for Martin to use more sliders and potentially generate more whiffs via the changeup, though his profile looks more like a streaming pitcher than a reliable starter in deeper leagues. The team context doesn't help him, but we can find sleeper starting pitchers playing on weaker teams. 

Yusei Kikuchi is Pumping More Sliders With the Astros

Over the past month, Kikuchi bumped up his slider usage since joining the Astros. Kikuchi threw his slider 14.2 percent of the time in June, 19.3 percent in July, and took a massive jump in August (35.9 percent). His slider peaked at 46.5 percent usage in September. The results against his slider improved since August 1, with a .223 wOBA, but the expected wOBA of .316 tells us to be slightly cautious.

That suggests Kikuchi's slider results might be more luck-based than skill, mainly via the BABIP (.239) and contact quality since August 1. When a pitcher throws a pitch more often, it sometimes leads to mixed results. That's the case with Kikuchi, though the surface numbers look solid.

We wondered if Kikuchi's slider shape has changed since joining the Astros. The downward movement in August was the most of any month of the season (32.9 inches) before September's boom at 34 inches and over 1-2 inches more than the season-long average (31.5 inches). We've seen Kikuchi's monthly slider movement profile shift by 1-2 inches, a normal fluctuation, but more downward movement can lead to whiffs.

If it's not a movement change, maybe it's related to location. From April to July, Kikuchi has been throwing the slider down and away from left-handed hitters or down and inside to righties (Zone 13) 38.8 percent of the time. When he throws the slider in Zone 13, the slider allows a .233 wOBA (.224 xwOBA).

It's a respectable slider against righties, with a .303 wOBA (.308 xwOBA). However, the results seem fluky against left-handed hitters, evidenced by a .213 wOBA (.329 xwOBA). With the Astros, Kikuchi throws the slider less often in the same spot, down and inside the right-handed hitters at 29.7 percent of the time compared to 38.8 percent before August 1 with the Blue Jays.

The results have been equally good compared to the previous months, a potential sign of sustainability if he continues to pepper it in Zone 13. While we're nitpicking a one-month sample of the slider, it looks like a concerted effort from Kikuchi and the Astros. Kikuchi throwing more sliders, thankfully, led to positive results.

Kikuchi's Changeup Added Horizontal Movement

We often think about Kikuchi as a pitcher who primarily throws a four-seamer, slider, and curveball. He has been throwing the changeup only to right-handed hitters 13.8 percent of the time. It's his best pitch against righties, with a .190 wOBA (.223 xwOBA).

Kikuchi's changeup added over three inches of downward movement to 12.7 inches in 2024. We've seen the changeup possess around 10 inches of arm-side movement, but it reached a career-high this season.

His changeup hasn't elicited more whiffs, with a 14.6 percent swinging strike rate in 2024 compared to a career average of 14.1 percent. However, Kikuchi's changeup generates weak contact against right-handed hitters. In 2021 and 2022, we saw his changeup perform well versus opposite-handed hitters, with 2023 as the outlier (.325 wOBA, .310 xwOBA).

When a pitch movement profile shifts, we guess it's related to a pitcher's release point. That's the case with Kikuchi's changeup. We've seen Kikuchi gradually lower his vertical release point over the past few seasons. From 2022 to 2023, Kikuchi's vertical release point dropped by over 1.5 inches.

Meanwhile, Kikuchi's horizontal release point might be more notable by nearly three inches in 2024 compared to 2023. That indicates Kikuchi's horizontal release point moved farther away from the midline of his body, sometimes leading to more horizontal pitch movement.

It might be a leap, but these release point changes over the past two seasons may have helped improve his control and develop better command of his pitches. While Kikuchi's walk rate improved, a better indicator involves his ball rate. Kikuchi's ball rate in 2021 and 2022 sat at 36.4 percent, similar to his control in 2023 and 2024 combined at 34.7 percent.

Summary

Kikuchi was dominant in August after joining the Astros, evidenced by a 2.57 ERA (2.79 xERA), 26 percent strikeout minus walk rate, and 15.2 percent swinging strike rate. Though it's a one-month sample, Kikuchi joining a new team and performing well doesn't seem like an accident.

It's been a positive change for Kikuchi to throw more sliders, but the expected stats suggest tempering expectations of it being a dominant pitch in 2025.

The changeup is an intriguing wild card, especially if it continues to be a successful offering against right-handed hitters. Though the haul for Kikuchi to the Blue Jays felt like the Astros overpaid, he might be a solid contributor for the starting rotation into the playoffs.

If Kikuchi continues to thrive to close out the final stretch and playoffs, his 2025 ADP won't be cheap, especially if the Astros re-sign him as an unrestricted free agent in 2025.

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