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ST LOUIS, MISSOURI - MAY 30: Kyle Leahy #62 of the St. Louis Cardinals pitches against the Chicago Cubs at Busch Stadium on May 30, 2026 in St Louis, Missouri. (Photo by Joe Puetz/Getty Images) | Getty Images
On June 12, Kyle Leahy completed his 13th start of the season, allowing four runs across five innings against the Twins. Once again, he had run out of gas the third time through the order, allowing all three batters he faced in the bottom of the sixth to reach base on a pair of doubles and a walk.
The clunker brought his season ERA to 4.64 and the underlying data was even more troubling. His xERA was 6.75, which ranked 106th out of 108 pitchers that had thrown at least 60 innings. His 92.5 mph average exit velocity allowed and 50% hard-hit rate were both second-worst marks in baseball. Opposing hitters were hammering Leahy to the tune of a .388 xwOBA. For perspective, a .388 xwOBA would rank 13th among qualified hitters in baseball. Leahy was essentially turning every batter into Ben Rice or Alec Burleson.
Much of the damage was coming later in starts as he was allowing a ghastly .615 xwOBA the third time through the lineup, though the first two turns through had not been anything special either. At this point, the move to the rotation was a resounding failure. If Leahy did not figure something out, his move back to the bullpen seemed a foregone conclusion.
Well, he appears to have figured something out.
In his last nine starts, Leahy has pitched to a 1.86 ERA. His advanced metrics, of course, do not support this level of dominance, but by any measure, he has performed like a top-20 starter in baseball over the stretch.
I know it is playing with fire to use arbitrary endpoints when evaluating any player, but I don’t remember ever seeing a switch flip this dramatically. In Leahy’s first 13 starts, he held opposing lineups to an xwOBA below .361 two times. In his last nine starts, he has held opponents below that mark all nine times.
Could he possibly keep this up? I sure hope so. Leahy is an extremely fun player to root for. He was basically a non-prospect coming up through the system and seemed to have maxed out his talents when he emerged as an effective reliever over the last two seasons. This trajectory of improving every season may have me irrationally optimistic, but the dude just keeps getting better.
*Note that the statistics referenced moving forward compare Leahy’s first 13 starts to the last eight before last night. Leahy’s xwOBA against the Rockies was the worst of his nine-start run (.361), but he had a season-high whiff rate of 31%.
Alright, so what has changed from Leahy’s forgettable start to his recent run of excellence? First, his stuff has taken a dramatic step forward during this stretch. His four-seam velocity is up from 93.8 mph in his first 13 starts to 94.7 mph. This increase is mirrored across his repertoire, with his sinker, changeup and curveball all increasing about 1 mph. The movement profile has changed as well. Leahy’s four-seam fastball is sinking 2.15 inches more in his recent starts and his sinker has added an additional 1.22 inches of sink. The Stuff+ model, which grades pitches based on velocity, movement, release point, and spin, with 100 representing league average, loves the changes. Leahy’s four-seam grade has increased from 85 to 90 and his sinker grade from 103 to 108. I should note that usually pitchers want to increase the rise on their four-seam. Leahy’s induced vertical break, or rise on his fastball, was almost exactly league average earlier in the season. An average movement profile with average velocity is usually not a good recipe. I would speculate that the added four-seam sink is unique enough in shape to be an improvement on the previous version of the pitch.
Stuff+ is all well and good, but how are the hitters grading the new and improved arsenal? Based on xwOBA, hitters are equally impressed with the recent version of Leahy.
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Leahy is always going to make his money with his breaking balls, but his four-seam has been playable and his sinker an outright weapon in recent starts. The more traditional batted ball statistics back up this improvement as well. Leahy has increased his groundball percentage from an average 42.8% to an excellent 48.2%. He has had some luck on flyballs with a 7.7% HR/FB ratio in his last eight starts, but even with a bit of regression there, he should still be able to limit home runs if he can keep his groundball rate this high.
Leahy has done some tweaking with his pitch mix as well by reducing his four-seam usage from 29% to 24%. Even though it has improved, the four-seam is still his worst pitch, so staying away from it as much as possible is ideal. This change to the pitch mix has made his repertoire ridiculously balanced as he is now throwing all six of his pitches between 13% and 24% of the time.
This balanced approach has been made possible by Leahy’s excellent command. He has never struggled with walks as a major leaguer, but BB/9 had climbed to a slightly above-average 3.52 during his early season struggles. Since then, he has walked just 2.08 per nine innings. He increased his percentage of pitches in the zone from 48% to 50%. Interestingly, he is not indiscriminately flooding the zone with all his pitches. He is actually throwing fewer strikes with his four-seam fastball going from 55% to 47% strike rate. To offset that, he is throwing his other pitches in the zone 51% of the time, up from 45% earlier in the year. This approach has given Leahy yet another way to shield his four-seam fastball from overexposure. The combination of throwing the pitch less often and throwing it for fewer strikes has reduced his rate of four-seam fastballs in the zone by almost a third.
Leahy has doubled down on the reduced fastball usage as he gets deeper into games. The third time through the order, his sweeper has been his most-used pitch at 20% with his four-seam usage dropping all the way to 19%. The approach seems to be working. Leahy has held opponents to a .313 xwOBA after turning the lineup for the third time.
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The biggest red flag in terms of Leahy’s production sustainability is that he is still not missing many bats. Despite the seemingly improved stuff and pitch mix, his chase rate and contact metrics have not wavered throughout the season and are still ranked near the bottom of the league. He has still been able to increase his strikeout production by pitching ahead more frequently and getting into favorable counts.
Are the improvements real?
Leahy has undoubtedly taken a step forward. His stuff has improved throughout the year and he is mixing his expansive repertoire to keep hitters guessing. Still, if he doesn’t start missing bats more reliably, he is going to be prone to stretches of bad batted-ball luck. In his current form, I am increasingly confident that he can be a No. 3 or No. 4 starter just by limiting walks and damage on contact. It does feel like there might be another gear here, though. Leahy’s four-seam was an above-average pitch last year as a reliever. If he can continue to build his velocity back up to 95+, that will take some of the pressure off his other pitches and allow him to save the breaking balls for two-strike counts. Pretty good for a non-prospect converted reliever.
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