Fantasy Baseball Starting Pitcher Arsenal Changes (Week 18): Pitch Mix, Velocity, and Movement

Corbin examines two fantasy baseball pitcher risers and sleepers displaying changes in their pitch mix, movement, and velocity heading into Week 18 (2024).

Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 18 of the 2024 fantasy baseball season. Today's article will discuss Reese Olson and Tobias Myers. 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 over halfway through the fantasy baseball season, causing fantasy managers to make crucial decisions for the second half of the season. 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 who may be included in a future article.

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Reese Olson's Slider is Nasty But Lost Horizontal Movement

Olson's slider highlights his arsenal, with a 20.4 percent swinging strike rate. That's similar to 2023, though it lost over two inches of horizontal movement. Olson's slider maintained its downward movement, aligning with the above-average swinging strike rate.

The slider has been dominant against right-handed hitters, with a .170 wOBA in 2024 compared to .290 wOBA in 2023. That indicates Olson's slider generates whiffs and weak contact in 2024 against righties. There's some luck in his favor against the slider, evidenced by his 6.3 percent HR/F in 2024 compared to 18.8 percent in 2023 and his .211 BABIP (2024) down from .274 (2023).

Olson peppers the slider down and away to right-handed hitters or low and inside to lefties around 47-48 percent of the time over the past two seasons. The slider allows a .266 wOBA when throwing the slider in Zone 14, which is down and below the zone away from right-handed hitters. Olson uses the above-average downward movement via the slider to elicit whiffs and weak contact.

Olson is Throwing More Changeups to Left-Handed Hitters

Olson lowered his four-seamer usage to lefties while increasing his changeups. His changeup went from his third-most used pitch at 19.8 percent to lefties in 2023 to 27.5 percent, as his second-most used offering in 2024. Olson's changeup swinging strike rate increased by over four percentage points from 2023 to 21.2 percent in 2024. He lowered the zone rate by a few points while hitters chased the changeup more often in 2024.

With the increased changeup usage against lefties, the results didn't improve. That's evident by the .232 wOBA in 2023 to a .308 wOBA in 2024 via Olson's changeup versus left-handed hitters. Olson's .264 xwOBA against left-handed hitters hints at better results, so we shouldn't overreact to the slight change in outcomes in 2024.

The movement profiles haven't changed much for Olson's changeup, so maybe there's a slight location change. Olson located the changeup below the zone a ton. However, he threw it more often down and below the zone in 2024. In 2023, Olson threw the changeup in Zones 13 and 14 below the zone over 63 percent of the time. However, he threw the changeup in those zones over 70 percent of the time in 2024.

Unsurprisingly, Olson's changeup dominated with a .061 wOBA in 2023 and a .110 wOBA in 2024 when thrown in Zones 13 and 14, down and below the zone. With the above-average vertical movement profile, Olson's changeup will be a weapon for whiffs and poor contact.

Summary

Last season, Olson's xERA (4.00) was identical to his actual (3.99). Olson's results and expected stats improved, evidenced by a 3.23 ERA versus a 3.67 xERA in 2024. While there has been some luck via the lower HR/F and higher strand rate in Olson's favor, his strikeout minus walk rate hovered near the 2023 numbers, with a slight increase in swinging strike rate. That indicates Olson's skills took a slight step forward, though we know players find success with a mixture of luck and supporting metrics. After drafting this write-up, Olson landed on the injured list with a shoulder injury, so hold where you can in deeper formats since he uses the slider and changeup as two effective pitches to each side of the plate.

Tobias Myers Bumped Up His Slider Usage in July

After Myers used his slider around 15-16 percent of the time from April to June, he doubled the usage in July to 30.9 percent. We're dealing with small samples since he barely threw it against left-handed hitters. However, it's worth noting Myers threw his slider around 3-4 percent of the time to left-handed hitters from April to May, jumping to 26.9 percent in June and 41.7 percent in July. The slider results improved and became unhittable against lefties in July, meaning we might have something actionable here.

Myers's slider leads his arsenal with a 16.3 percent swinging strike rate similar to his changeup swinging strike rate (16.3 percent). The changeup usage remained steady throughout the 2024 season and has been dominant against left-handed hitters. That's evident by the .161 wOBA via the changeup versus lefties, as his best pitch that he throws over 10 percent of the time.

Myers Might Have a Good Four-Seam Fastball

Myers's four-seamer possesses an above-average movement profile, mainly via vertical movement. The four-seamer generates tons of induced vertical break (IVB) at 19.1 inches, though it lacks mediocre arm-side movement of 4.7 inches. Theoretically, Myers's four-seamer should generate weak contact and whiffs. Unfortunately, the four-seam elicits an 8.2 percent swinging strike rate but decent results against right-handed hitters, with a .269 wOBA, while the four-seam struggles against lefties (.383 wOBA).

Given the four-seamer's average to above-average vertical approach angle of -4.7 degrees, Myers might struggle with the location of the fastball. Myers lost a couple of inches of IVB in July compared to 19-20 inches from April to June. Since Myers' release points haven't changed month by month, his four-seam IVB should bounce back closer to the previous months. 

Summary

Myers' xERA of 3.99 sits almost one run higher than his actual outcomes (3.14). He has been lucky via his strand rate (79 percent). However, his skills suggest he's an average to slightly above-average streaming pitcher based on the matchups. Bake in regression for Myers, though we'll take mediocre to above-average streaming pitcher for the rest of the season. The bump in slider usage in June and July looks actionable, especially paired with the changeup eliciting an above-average rate of whiffs. 

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