A deep dive on the Cardinals’ reliever who is assuming higher leverage roles
I am back with a second pitcher breakdown article. Includes charts and dense statistics. You are warned! I picked Kyle Leahy as he has moved from back-end “chase” reliever on the Memphis shuttle to more high-leverage situations since last year, and I want to know more about how he has improved. Hopefully, we have enough data to look at this year, as his historical data is much scanter than my prior subject – Phil Maton. As always, the discussion and debate are half the fun.
Demographics
Although he feels young, Kyle Leahy is playing in his age-27 season. He still rates as inexperienced, with 2024 being a bit more than half a season work-load wise (48 IP) and 2025 portending to be his first full season. He was drafted by the Cardinals back in 2018, making that draft class look even better. They found him at a veritable baseball backwater, Colorado Mesa U. in Grand Junction, CO. The Rockies probably would like him, as he certainly knows how to pitch at altitude.
Leahy has pretty much been a reliever since he had two not very good starting seasons at AA (2021 and 2022), so they converted him to reliever and promoted him to AAA. Typically, this happens with a pitcher who doesn’t have a deep enough arsenal but has one or two quality pitches that profiles better for a short-stint reliever. Leahy does not appear to fit that archetype, as he has a deep arsenal. He really is two different pitchers … one against left-handed and another against right-handed hitters. More on that later.
Coming into 2025, he has accumulated 140 days of service time (180 is a full year), so he has 6 full years of control before FA, so he will likely be with STL through his age 32 season (with all the usual caveats about reliever volatility).
Most of the article will focus on 2025 data but will reference back a little bit to 2024 where support can be found or questions arise.
League-wide Pitcher Comparison
Leahy’s 2024 rankings against other MLB pitchers isn’t shown because most of the ratings show as not enough data. His current 2025 profile is shown below.
Data and image courtesy of Statcast | Baseball Savant
Good stuff. Always nice to see lots of red for the boys who wear red, so I see lots to like. A couple of things stand out to me.
How about that oddity of being 35th percentile chase rate, 18th percentile whiff rate yet 76th in K rate. Something there doesn’t seem quite sustainable. Seems like either he gets a ton of struck-out-looking or he gets all his whiffs with 2 strikes.
Or how about that 14th percentile barrel rate (not good) compared to that 71st percentile average exit velocity? How does he give up way more than average barrels, but get way above average weak contact at the same time?
I like his walk rate as a pitcher, and his elite extension probably allows an above-average fastball to play up closer to really, really good fastball. This is good, because so far this year, he appears to be a full tick below last year’s FB velo. Overall, positive run value for the FB, and really good run value for his breaking stuff. Combined with a low walk rate that’s a really nice reliever.
Pitch Movement
In looking at Kyle’s pitch movement charts, the first thing that pops up is how many pitches he throws. Six is a lot for a reliever. It’s really a lot for even a starter. Until I saw his AA starter numbers, I wondered why he isn’t a starter. 8.20 ERA in 20+ starts in AA is … not good, even by Springfield standards. He repeated the level another year and the results were similarly bad. I’m guessing he was a different pitcher back then.
Data and image courtesy of Statcast | Baseball Savant
The fastball has above average velo, and above average vertical break. In other words, it has a hop (or a ride or carry) to it at the end. This pitch profiles to produce more than a few K’s and some pop-ups to boot. A little bit more horizontal movement wouldn’t hurt him though. While being above average, the results are more average-ish than other pitches he has, with a -1 run value.
In 2025, Leahy has introduced a new version of his fastball. Last year he threw four-seam FB 40% of the time. This year, he has dropped that to ~33% and traded them in for a new pitch, the sinker (which I believe is just a two-seam FB, no?). As noted below, that sinker is very effective against RH hitters and probably helps his 4-seamer play up a bit. The sinker and the 4-seamer come out of his hand the same in terms of spin AND velo, but the differences in movement the batter experiences late in the pitch cycle appears to be just enough to throw them off. The 4-seamer hops a bit more, the sinker bores in on the hands of RH hitters more.
Of his pitch mix, he reserves his sweeper, slider and sinker for RH hitters. He reserves his change and curveball for LH hitters, and throws the 4-seamer to both sides, with a little bias towards the LH hitters. So, really, he is two different pitchers in one, depending on the handedness of the hitter.
One thing Leahy does well is hitters have a very hard time pulling the ball in the air against him. His pulled in the air rate is roughly half of league average. If I had a guy on third and less than two out, he might be the guy I want out there, because the batter is less likely to get the ball into the outfield, his GB% is solid and plays to the Cardinals defensive strength on the infield.
Both his sinker and sweeper are pretty effective against RH hitters. Almost every one of those pitches he has thrown this year has been average or better. Good and consistent is pretty good. Both pitches rate out very well in terms of horizontal break. That sweeper is generating a 30% whiff rate.
By Stuff+, Leahy is roughly league average (no insult). Since his debut, he has progressed his Stuff+ from 80 to 90 and now to ~100. By Stuff+ his slider rates out as his best pitch (104), He combines with a Location+ rating of 112 (very nice, thank you) for an overall Pitcher+ rating of 114. He rated 107 last year, so he came in with above average stuff and has tuned it yet even more.
Leahy against LH hitters
HIs curveball is a super effective pitch. It has 5” more vertical drop that league average and 3” more horizontal break than league average (that measly 3” is 30% better than average). Curiously, it doesn’t generate much whiff, but boy batters beat it into the ground at an average launch angle of -38 degrees. His expected SLG on this pitch is .118 this year, was .338 last year. Something to watch.
His change and curveball play off well against each other. There is a full on 180-degree gap (shown in Statcast as 6 hours on a clock face) between these two. This gap is second in the league, trailing only a dude named Skenes. I think this roughly means that the spin looks the same to the batter (making it hard to assess what the pitch is) but at some point down the pitch lane, the ball veers in opposite directions, leaving the LH hitter little time to adjust if they guess wrong. That data set on curves and changes against LH hitters is a bit too small to evaluate, so something to watch through the season. If it holds, I imagine he will be quite effective against LH hitters.
Run values
Run value assesses how a pitcher actually performs with a specific pitch. It’s a bit early to draw too many conclusions, since this is a counting stat and the sample size is way small. Near as I can tell, relievers may not throw enough of a pitch in a season to get outside the SSS boundary.
Be that as it may, it tells us a little something. For instance, Leahy leads the team in total Run Value on his pitches (+5) despite (or maybe because of) having the fewest PAs. The others in the top 5? Matz, Maton, Gray, Liberatore. What this stat tells you is what you already know. He has pitched well.
Interestingly, if you evaluate the quality of his pitch arsenal (using RV/100), 3 of his pitches are in the top 10 of the Cardinal staff, alongside pitches we know such as Pallante’s slider and Maton’s cutter. These stats aren’t predictive, but they do tend to confirm the notion that he has a pretty wide arsenal. He is the only Cardinal pitcher with 3 in the top 10.
Platoon Splits and Usage Profile
The sample size is a bit too small to say what platoon splits might exist. As commented above, he seems to have weapons to get hitters from both sides of the plate out. There is enough history there that I suspect that Oli doesn’t look at him as a 3-and-done reliever and doesn’t worry too much about nursing him through those 3 batters he is required to face.
Leahy projects as a multi-inning reliever, given his assortment of pitches. Given the challenges Roycroft and Fernandez have had bridging to Maton and Helsley, it isn’t hard to imagine Leahy moving into even higher leverage situations.
Let’s stop for a drink at the Sidebar for a moment
A comment on sample sizes here … recalling a prior article on the Brewers and how they succeed. One thing they do well is evaluate actual player performance and make adjustments quickly. The Cardinals tend to want to gather more data and broaden the sample size before concluding. Both are valid, but I suspect with relievers, their exposure is so low that it really is better to make fast conclusions based on limited data and actual results than wait for more certainty in a large sample size. By the time you get enough data for it to be stable and predictive, too much season has gone by and perhaps too much damage done.
I noticed this while compiling Leahy’s stats. As an example (I write this on April 21), it is clear from a run value perspective that Ryan Fernandez has a problem with his slider, which is (was?) his go-to pitch. The run value of his slider is 740th out of 746 pitcher/pitch combinations (min of 50 pitches), with a run value of -5. That number would be a problem in June, much less April. He could pitch to a neutral run value for the rest of the year, and he’d still finish in the bottom 10th percentile of the league (using full season 2024 as the comp). And that is with his best pitch.
Since his results are from a mere 67 pitches, one could argue SSS all day and not be wrong. Some might say, let’s wait until 200 pitches and see if it stabilizes. Of course, it’ll be late May, early June before that happens and one has to wonder how many games will go sideways as a consequence. In reliever-land, I’d wonder if there’s enough data to conclude that’s a problem that needs addressed before there are more dumpster fires out there. Reliever volatility is a pain to evaluate, huh?
Ok. End of tangent. Now back to our regular broadcast.
Summary
Kyle Leahy. Excellent command. Wide arsenal useful against both LH and RH hitters. No single “out” pitch, nothing elite. Profiles to a multi-inning reliever who can wiggle out of jams and take on higher-leverage assignments. Probably not closer material, absent that one elite level pitch, but very useful, nonetheless. I’d tend to think of him as the reliever version of “Jack of all trades, master of none”.
Total Sidebar
I’m kicking around the idea of coming into STL for Blogger Day on June 7. I haven’t been to St. Louis since Ryan Ludwick broke out (2007?), so I want to reach out for some ideas:
- Where should I stay the two nights I’d be in town (downtown? the burbs? the airport?)
- Is there light rail from downtown to the airport now? Recommended or avoid?
- If I stayed downtown, suggestions as to where? Or what to avoid?
- Where to eat down there? Is Laclede’s Landing still a thing?
- I’d kinda like to drive around a bit Saturday afternoon/night and see old stomping grounds (Florissant, Chesterfield, Maryville U.). Can I rent a car downtown for a day?
- Is The Hill still a thing?
Give me options….