Is it Legit? 6/11/24: Jack Flaherty, Luke Weaver, and Steven Kwan

Are Jack Flaherty, Luke Weaver, and Steven Kwan for real?

We are somehow getting close to the midpoint of the season. For most guys, we have plenty of data to be confident in. Here are some players that are playing well. Let’s see if it makes sense to be aggressive in picking them up, or buying/selling them.


Jack Flaherty, SP, Detroit Tigers


After spending much of 2021-2022 dealing with shoulder injuries and a poor 2023 Flaherty is in the midst of an unexpected career resurgence. Through 72.2 IP he has a 3.22 ERA, 0.96 WHIP, 33.5% K%, and 3.6% BB%. That 29.9% K%-BB% is best amongst qualified pitchers. Those numbers are supported by a 16.2% Swinging Strike% (97th percentile), 35.7% CSW% (100th percentile), and 35.1% ICR (83rd percentile). His expected ERA metrics range from 2.10 to 2.70, suggesting he has been unlucky. 

In 144.1 IP in 2023 he posted a 4.99 ERA, 1.58 WHIP, 22.8% K%, and 10.2% BB%. Has he simply fully regained his strength and command?

His four-seam velo has remained consistent throughout his career, hovering around 93.0-93.5 mph. The velocity on all of his other pitches has largely stayed the same, despite the injuries. Stuff+ has graded his repertoire similarly in 2023-2024. His primary pitches are the four-seamer (41%), slider (29%), and curveball (17%) and the movement profiles on them have been steady. Even his pitch usage has remained remarkably consistent. His slider usage has increased by 4%, but that’s not much.

That leaves just location. FanGraphs’ overall Location+ has increased from 99 in 2023 to 104 this year. Both Location+ and plvLoc+ agree that the slider and curveball locations have improved slightly. The biggest location riser is his four-seamer. Location+ gives it an increase from 99 in 2023 to 108 in 2024 and plvLoc+ gives it an increase from 99 to 105. A strong command improvement over a pitch you throw over 40% is quite valuable. The Zone% on it has increased by 7.3%. It is now up to 57.8% (87th percentile). It also has a Strike% of 70.9% (87th percentile).

The zone proficiency on his four-seamer has allowed him to expand with his breaking balls. The slider has a Zone% of just 29.0% (7th percentile) and the curve is 29.3% (11th percentile), and batters are chasing them. The slider has a 41.2% O-Swing%(83rd percentile) and the curve is 44.3% (94th percentile).

Verdict: Not Legit. The sudden increase of success for Flaherty is driven largely by O-Swings on breaking pitches in the Chase zone. I’m not sure there are many pitchers who have a greater difference in Zone% between fastball and breaking pitches. You’d have to think guys will catch on not to swing at pitches with any bend. I don’t doubt that his improved command should lead to better results. I should also mention he stopped throwing his cutter. Last year it had a 9% usage and a .406 wOBA. However, nothing like this. His overall velocity and stuff have remained the same. I don’t believe his K%-BB% or other excellent outcomes have been warranted.


Luke Weaver, RP, New York Yankees


This one is for holds leagues unless Luke Weaver finds himself in a position to get saves due to injury. Coming into this season 106 of Weaver’s 144 career appearances came as a starting pitcher, so he is essentially a failed starter. His best season came in 2019 for Arizona when he started 12 games and finished with a 2.94 ERA, 1.07 WHIP, 26.5% K%, and 5.4% BB%. The rest of his seasons range from passable to atrocious. He’s spent much of his career injured, but for a lot of it he was also just bad.

He was briefly in the organization at the end of the 2023 season and resigned with the Yankees in January 2024. Many, including myself, assumed he was just a depth starter in case of multiple injuries. However, he made the club out of spring training and went straight to the bullpen.

He has thrown 40.0 IP across 24 appearances and has posted a 2.70 ERA, 0.70 WHIP, 27.8% K%, 4.6% BB%, and 8 Holds. All of those numbers are career bests. Most pitchers have better numbers as relievers, but usually not as stark as this.

In previous seasons he threw as many as 6 pitches but has whittled his repertoire down to just a four-seamer (45%), cutter (29%), and changeup (25%). In previous seasons he threw his cutter between 3-12%. His current version of the cutter began to take form last year, but he only threw it 11% of the time. It averages 90.9 mph (71st percentile) and 12.5″ of Total Break (92nd percentile). Basically, he throws it pretty hard and it gets strong movement. Always a good combination. He throws it up and away to RHBs a lot too. It has a 46.1% hiLoc% and 73.0% oLoc% to RHBs, both 88th percentile. It also has a 71.5% PLUS% (89th percentile). That’s a measure of how often it has a positive outcome for the pitcher.

His other two pitches aren’t just along for the ride. His changeup has a 25.0% Swinging Strike% (90th percentile) and an 84th percentile ICR. His fastball hasn’t been quite as good, but OK. He also tunnels it with his cutter as both are thrown up and away a lot. The four-seamer has 17.9″ iVB (94th percentile).

Verdict: Legit. From 2022-2023 his overall Stuff+ was 95. In 2024 it is 119. Pair this with a 101 Location+ and you have an above average reliever. The Yankees have a history of turning middling pitchers into good relievers and Weaver may be the next. Long-term, is it possible Weaver can take what he’s learned as an RP and become a better SP?


Steven Kwan, OF, Cleveland Guardians


Since coming up in 2022 Kwan has been known as a very good contact hitter that steals bases but has virtually no power. In 2024 he hasn’t exactly turned into Rob Deer, but his power numbers have jumped.


Kwan Power


Seeing an uptick in young players as they age and get stronger isn’t surprising, but doing it while improving K% and AVG is.

Verdict: Not Legit. There isn’t any need to write a bunch just to make this longer. His Max EV has not increased, his Fly Ball EV has not increased, his Launch Angle has not increased, and his Pull% has not increased. His FB% and Brl% have increased slightly, but they don’t come close to explaining the 42-point increase in ISO. As far as I can tell he’s jumped 4 pitches for home runs. In fact, his hamstring injury may result in him running less. I have no doubt Kwan will continue to be a great contact guy with excellent plate skills, but I wouldn’t be surprised if he still finishes with fewer than 10 HR this year. Maybe you can convince someone to trade for him thinking they’re getting a high AVG with OK power, rather than the old Kwan.


Featured image by Doug Carlin (@bdougals on Twitter)

Andrew Krutz

Andrew writes for Pitcher List and is a lifelong New York Yankees fan. During the warmer months he can be found playing vintage baseball in the Catskill Mountains of Upstate New York.

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