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Welcome back, RotoBallers, to my weekly "Starting Pitcher Arsenal Changes" article series for Week 11 of the 2024 fantasy baseball season. Today's article will discuss Reynaldo Lopez, Ryan Weathers, and Gavin Stone. 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 a handful of 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.
After examining the changes for these starting pitchers in the early parts of the 2024 season, we'll summarize whether we should act or be patient with the data. We're two months into the season with a decent sample size of starts in 2024, and we'll compare the current and past information. This one is a bit beefier than usual and for a good reason.
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Reynaldo Lopez's Four-Seamer Changes
It's been a rocky path from starter to reliever and back again for Lopez. With the White Sox and other teams, Lopez performed well as a reliever. From 2021 to 2023, Lopez posted a 3.14 ERA, 1.06 WHIP, 26.7 percent strikeout rate, and 7.7 percent walk rate across 189 innings. It can be challenging for a reliever to transition to a starter, though sometimes the strikeout stuff remains nasty.
As a starter, we've seen Lopez's four-seamer velocity decline to 95.3 mph, and it's expected with the transition. Interestingly, Lopez's four-seamer hasn't generated the same level of arm-side run as in past seasons. His four-seamer's induced vertical break (IVB) of 16.7 inches is close to recent years, but it lost about 1-2 inches of horizontal movement.
Lopez's vertical and horizontal release points shifted by about one inch on the four-seamer. That's somewhat insignificant, and the velocity changes have contributed to the movement profile shift. Since Lopez's four-seamer changed, the results haven't been as fruitful. Lopez's four-seamer elicited a 12-13 percent swinging strike rate in 2022 and 2023, dropping to 5.8 percent in 2024.
The first hypothesis is a location issue for the four-seamer, but it looks like Lopez is locating the fastball in a similar area in 2024 compared to the previous two seasons. He tends to throw the four-seamer high and outside to left-handed hitters. Theoretically, Lopez's four-seamer should perform more like the 2022 and 2023 numbers, given the IVB and location with its average-ish vertical approach angle (VAA). However, the velocity is the main difference.
Most of the damage against the four-seamer comes from left-handed hitters. In 2024, Lopez's four-seamer had a .364 wOBA and 5.8 percent swinging strike rate against lefties. For context, his four-seamer posted a .307 wOBA and 14 percent swinging strike rate in 2022 and a .307 wOBA and 13 percent swinging strike rate in 2023. It's interesting to see lefties crush the four-seamer in areas where he throws it most often, though it aligns with the dip in whiffs.
The Slider is Dropping More
Lopez's slider is dropping more in 2024, with a career-high swinging strike rate of 24 percent. That's nearly seven percentage points above his career average. Theoretically, a pitch that drops more should induce more swings and misses. It's worth noting Lopez's slider vertical movement shifted significantly, with over five inches of drop.
The location seems optimal, as he throws it down and away from right-handed hitters or low and inside to lefties. Thankfully, Lopez's slider performs well against both sides of the plate. Against right-handed hitters, his slider boasts an elite .171 wOBA with a .117 wOBA versus lefties. Though there's some luck in his favor with a .238 BABIP in 2024 compared to a career average of .281, the skills and movement profile indicate an above-average slider.
Summary
It's a mixed bag with Lopez with luck factors in his favor (strand rate, BABIP), though he rocks an above-average swinging strike rate. On a pitch level, Lopez's four-seamer has been struggling with some minor movement changes. The velocity might be impacting his ability to generate whiffs and weak contact. However, Lopez's slider looks dirty, with tons more vertical movement supporting the swinging strike rate gains. While we didn't discuss the curveball in-depth, it might be the wild card to monitor since he throws it 17.3 percent of the time to left-handed hitters with a .170 wOBA allowed. Lopez's curveball doesn't generate a high swinging strike rate but can steal called strikes.
Ryan Weathers' Changeup is Dropping More
Weathers hasn't been known for the swinging strike rates, but we've seen more strikeout upside in 2024. Before 2024, Weathers hadn't reached 15+ whiffs in a game. However, he posted three games with 15+ whiffs with a career high of 21 against the Rangers on June 1.
His changeup elicited a 35.1 percent swinging strike rate, nearly double of his season-long average of 18.4 percent. There's a reason for his changeup generating more swings and misses. Weathers' changeup has been dropping over five inches more with an inch more arm-side fade.
That's significant because his changeup goes from a below-average pitch to an average or slightly above-average one. With the added drop, the changeup's ground-ball rate spiked to 57.7 percent, over seven points higher than in 2023.
Besides the swinging strike rate increase on the changeup, the results improved against right-handed hitters, with a .245 wOBA (2024) compared to a .340 wOBA (2023). Unfortunately, it's Weathers' only pitch with a wOBA below .300 against opposite-handed hitters, meaning he needs it to remain effective.
Meanwhile, lefties crush the changeup with an awful .433 wOBA, though the .238 xwOBA suggests better results. It has been performing slightly better than in 2023 when Weathers allowed a .683 wOBA and .454 xwOBA versus left-handed hitters on the changeup.
It's unsurprising to find the changeup struggling against left-handed hitters because he tends to locate it down and inside with arm-side fade to same-handed hitters. We'll note that opposing offenses stack right-handed hitters against Weathers, so we're dealing with a small sample, and this might be a moot point.
Why is the Sweeper Better?
Weathers' sweeper has been performing better from a swinging strike rate of 15.6 percent compared to 11 percent in 2023. The same trend occurs in batted-ball results, with the most significant jump against right-handed hitters. His sweeper allows a .299 wOBA in 2024 versus a .423 wOBA in 2023. The results look even better against left-handed hitters with a .203 wOBA (2023) and a .104 wOBA (2024).
Since it's been nearly unhittable, there's likely a movement profile change. Weathers' sweeper added 1.5 mph of velocity, and it's been dropping 2.5 inches less. The sweeper typically isn't used for generating whiffs with a league-average 13.7 percent swinging strike rate. However, it tends to help induce weak contact. Since the sweeper movement profile hasn't changed much while gaining whiffs, there's possibly a location change.
Weathers has been throwing the sweeper nearly 12 percentage points down and inside to right-handed hitters. That's a sweet spot for the sweeper, allowing a .238 wOBA in 2024, similar to a .193 wOBA in 2023. Like the changeup, Weathers' sweeper contributes to the ground-ball rate skyrocketing, evidenced by the 50 percent ground-ball rate in 2024, over 20 points above 2023.
That's a positive change in location, leading to more ground balls and continued weaker contact. So why not throw the changeup more outside the zone, low, and inside to right-handed hitters? That's what Weathers has been doing. He throws the sweeper more outside the zone with a 37.5 percent zone rate, seven points fewer than in 2023, and hitters haven't been making contact (46.2 percent contact rate).
Summary
Weathers looks like he's evolving in 2024 (with most of his results being earned) with some regression, given his 3.75 xERA. His spike in ground-ball rate via the changeup and sweeper helps keep the home runs in check. A pitcher generating more ground balls with the changeup and a sweeper working well for whiffs and weak contact feels like a discount version of Ranger Suarez or Cristopher Sanchez. Weathers doesn't have the sinker like Suarez and Sanchez, but maybe he'll want to add it to his arsenal.
Gavin Stone is Throwing More Sliders
Stone logged 15 or more whiffs for the third time in his career after 15 against the Rockies on June 2. He threw the slider 25 percent of the time, the second most often. Stone's slider elicited a 47.4 percent swinging strike rate versus the Rockies, over double his season-long average (22.3 percent).
He threw the slider at a season-high rate with a previous high of 22.2 percent. Since Stone's slider has been one of his top two best pitches for generating whiffs in addition to the changeup, it's positive to see him use the breaking ball more often.
Stone's slider velocity increased by nearly 3 mph. Unsurprisingly, his slider lost four inches of vertical movement and four inches of horizontal glove-side sweep. However, it's interesting that his slider induces more swings and misses while losing movement to its profile. That's likely due to location changes on the slider.
It's worth noting we're dealing with small samples in 2023 and 2024. Stone locates his slider down and away outside the zone from right-handed hitters and finds success. He lowered the zone rate on the slider from 57.5 percent (2023) to 53.8 percent in 2024, causing hitters to chase and whiff more often. The results improved against righties versus the slider with a .223 wOBA compared to .353 in 2023, though the .318 xwOBA in 2024 hints at some regression.
Stone's Deadly Changeup
It sometimes causes us to pause when a starting pitcher relies heavily on their changeup, which Stone tends to do, throwing it 26 percent of the time in 2024. However, Stone evenly mixes with the sinker (24.6 percent) and four-seamer (23.9 percent) with the changeup, so it's not an overreliance on the off-speed pitch.
Stone's changeup has been deadly with an 18.8 percent swinging strike rate, down over five percentage points in 2023. He lowered his zone rate on the changeup to 31.7 percent, over 12 percentage points below 2023. Stone's changeup stifles left-handed hitters, evidenced by a .192 wOBA in 2024 compared to .321 in 2023. He throws it about 1 mph harder with slight and insignificant movement profile changes.
Like the slider, there's a location difference for the changeup. The location changes allow the slider and changeup to perform better in 2024, meaning non-fastballs can attack both sides of the plate.
Summary
Stone has been relatively efficient, averaging 86 pitches and 5.7 innings per start. That's likely something that continues, though he threw 124 innings in the minors plus 31 more in 2023, so he can handle a moderate workload. He might not have the near-elite stuff to generate tons of strikeouts, but he boasts solid control, with a 34.4 percent ball rate. Expect some regression with his xERA about a run higher than his actual, but the deadly changeup paired with the slider location leading to more whiffs and weak contact gives us more confidence.
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