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Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 15 of the 2024 fantasy baseball season. Today's article will discuss Casey Mize and Spencer Schwellenbach. 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're halfway through the fantasy baseball season, nearing the All-Star break, causing fantasy managers to make crucial decisions for the second half of the season. With rookies like Schwellenbach, I tend to give them about a month to gather enough data to make actionable decisions. Meanwhile, we're looking at the successes or struggles of other starting pitchers to understand the why.
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Casey Mize's Slider is Dropping More
In Mize's start against the Phillies, he posted a career-high 10 strikeouts across 4.1 innings, with a career-best 20 whiffs in a game. Mize's slider added three inches of vertical break compared to the season-long average, translating into a 19.4 percent swinging strike rate on June 24. His whiffs disappeared again when he threw 5.1 scoreless innings against the Angels, but the slider's vertical movement intrigues us.
We're dealing with small samples for Mize, with only one season of more than 100 innings in 2021 (150.1). When we use 2021 as the baseline, Mize's slider dropped nearly 35 inches (34.9), increasing by over two inches to 37.2 in 2024. Weirdly, Mize's slider hasn't elicited many whiffs, with a 7.4 percent swinging strike rate on the season and 9.6 percent in his career.
Though the slider's vertical movement fluctuated slightly throughout 2024, it appears relatively stable, potentially leading to more whiffs moving forward. Mize's vertical release point increased to the highest point since May 2021. Meanwhile, Mize's horizontal release shifted closer to the midline of his body, but the vertical release seems to be contributing more to the added downward movement.
If Mize's slider doesn't elicit whiffs, we hope it improves in generating weak contact. Unfortunately, that's not the case, with the slider allowing a .374 wOBA against right-handed hitters and better versus lefties, with a .216 wOBA. Mize's slider has been his most effective pitch against left-handed hitters, as he tends to locate it down and inside to opposite-handed hitters.
We've seen a slight uptick in swings and misses via the slider, with a 5 percent swinging strike rate in March/April to 8.1 percent in May and 10.9 percent in June. Let's see if Mize's slider continues to add downward movement and generate average swing-and-miss rates since he needs something to pair with the splitter.
Mize's Splitter Lost Downward Movement, But Gained Whiffs
The profile for Mize is quite odd. Typically, when a pitch adds downward movement, it should elicit more whiffs and weaker contact. However, we see the opposite effect with the slider and the splitter. Mize's splitter lost 3-5 inches of vertical movement compared to 2022 and 2021. That makes his splitter go from an above-average movement profile in vertical drop to mediocre.
However, Mize's splitter does possess above-average arm-side fade, with 13.1 inches of horizontal movement. His splitter elicits a swinging strike rate of 16.7 percent, over three percentage points above his career average (13.1 percent). Mize throws his splitter most often against left-handed hitters, allowing a solid .280 wOBA in 2024.
Besides the added horizontal movement, we might speculate on the splitter's location. From 2020-2022, Mize threw his splitter down and inside the left-handed hitters 31.5 percent of the time. Meanwhile, he tossed the splitter down and away from left-handed hitters or low and inside the righties at 14.8 percent.
In 2024, Mize has been throwing his splitter 46.5 percent of the time in Zones 13 and 14, down and outside the zone on either side of the plate. Hopefully, Mize continues to locate the splitter in those areas outside the zone because it allows a combined .103 wOBA in 2024, similar to his career average of a .144 wOBA.
Summary
Mize is a strange starting pitcher who elicits whiffs at a below-average rate (9.5 percent) with a decent 35.2 percent ball rate. From a stuff and movement profile standpoint, only his slider, curveball, and splitter possess above-average movement profiles. Only Mize's splitter generates a double-digit swinging strike rate, though it lost vertical movement.
Keep tabs on the slider because it could give him an average to slightly-above-average pitch with the added downward movement, especially against left-handed hitters. Unfortunately, Mize left his most recent start with a hamstring issue and will head to the injured list, so file away this column on him.
Spencer Schwellenbach Has a Nasty Slider
It's tricky to break down a starting pitcher with only 31.2 innings, but Spencer Schwellenbach warrants our attention. Schwellenbach's slider possesses over 40 inches of downward movement, making it an above-average breaking ball. His slider elicits a 15.7 percent swinging strike rate, hovering near the league average (16 percent). The slider generates weak contact with a .233 wOBA.
Schwellenbach throws his slider most often against right-handed hitters (34.4 percent of the time), with positive results (.239 wOBA). As a prospect, Schwellenbach's slider was one of his best-graded pitches as a plus-offering. He locates the slider down and away outside the zone from right-handed hitters 41.7 percent of the time, allowing a reasonable .276 wOBA.
Interestingly, Schwellenbach's slider performs better in the zone, evidenced by a .190 wOBA compared to outside the zone (.280 wOBA). His above-average extension and low vertical release point might help his slider be an effective breaker in the zone, especially considering the downward movement and spin he generates.
The visual below shows the right-handed starting pitchers sorted by the lowest vertical release point, with a minimum of 50 sliders and 500 total pitches.
Schwellenbach's horizontal release point (-2.87) is slightly farther away from the midline of his body, giving him a low three-quarters arm slot, nearly similar to Freddy Peralta (-3.17). Given Schwellenbach's vertical and horizontal release points, his slider may or should possess more sweep. Nevertheless, the slider movement profile is nasty, allowing weak contact, but we should project more whiffs soon.
Schwellenbach's Splitter Shoves
Sorry for the alliteration, but Schwellenbach's splitter elicits the third-highest whiff rate among right-handed starting pitchers in 2024. He threw 54 of his 56 splitters to left-handed hitters (18.1 percent), his fourth-most-used pitch, resulting in a .234 wOBA. When Schwellenbach's splitter works well, it drops nearly 38 inches (37.7), with over nine inches of arm-side fade.
Hitters have chased the splitter 45.2 percent of the time, aligning with the ridiculous 28.6 percent swinging strike rate. Schwellenbach's splitter swinging strike rate sits over 10 percentage points above the league average, making it an elite whiff offering. It's a small sample of pitches thrown, but Schwellenbach's splitter allowed one hit (single) when thrown outside the zone. His splitter falls off the table and under the barrel of left-handed hitters.
Summary
Since Schwellenbach doesn't have a good fastball from an induced vertical break perspective, given the 13 inches of IVB, he needs quality non-fastballs. Though Schwellenbach's slider elicits a decent swinging strike rate, it's near the league norm. However, Schwellenbach's slider movement profile indicates an above-average pitch, and whiffs could be coming. Meanwhile, his splitter is nasty and nearly unhittable so far.
The low release point, three-quarters arm slot, and high-end extension help the pitches thrive, especially the slider and splitter, giving the hitters little time to react and adjust. We've been chasing starting pitcher prospects for the Braves for a while, including AJ Smith-Shawver, Hurston Waldrep, Bryce Elder, Dylan Dodd, and Ian Anderson, to name a few. However, Schwellenbach looks like the one to buy into since the above-average skills exist while needing the luck factors to shift in his favor.
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