ANALYSIS: Underlying Stats Might Explain Reliever's Up-And-Down Season
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SEATTLE — The Seattle Mariners bullpen has been one of the most chaotic units on the team this season.
The bullpen has had several injuries, was one of the most heavily-taxed units in baseball earlier in the season, and has had several relievers make their major league debuts this year.
The Mariners' high-leverage arms have been solid-to-elite for the majority of the season, but the middle-inning and low-leverage relievers have been more volatile.
One of the most volatile performers has been Casey Legumina. The third-year reliever is currently in his first season with Seattle. He's had genuinely impressive outings, but has also had some poor ones. His month-by-month splits demonstrate that.
In April, Legumina had a 3.52 ERA in eight appearances. He had a 5.25 ERA in 12 appearances in May, a 1.38 ERA in 11 outings in June and a 24.92 ERA in five appearances in July entering Tuesday.
Legumina's last two appearances are also a perfect micro view of his season. He had three strikeouts in one inning with no walks or hits against the Houston Astros on July 19. He followed that with four earned runs on three hits in an inning pitched against the Astros on July 20.
This has translated to a season ERA of 5.84 for Legumina with 41 strikeouts in 37 innings pitched across 36 appearances entering Tuesday.
Casey Legumina start of 2025:
— Steve (@MarinersSteve) May 22, 2025
17 G / 16.2 IP
17 K / .168 OPP AVG
1.62 ERApic.twitter.com/jeGMOT2CM6
Legumina is better than his surface stats indicate, so let's go under the hood.
The former Gonzaga product has a four-pitch mix including a four-seam fastball, sweeper, two-seam fastball (sinker) and changeup.
Legumina's received balanced results from all four offerings. The only pitch he's allowed more than a .250 batting average with is his sweeper (.258), per Baseball Savant. He has a put-away rate of 19.8% or better on three-of-four pitches. Legumina has thrown his four-seamer the most (361 times), followed by his sweeper (115), sinker (79) and changeup (76).
From a numbers standpoint, Legumina's changeup is his best offering. He's allowed an opposing batting average of .190 with it, has generated a whiff rate of 14.3% and has a 21.8% put away-rate with it — the highest put-away rate in his arsenal. He throws it predominantly against lefties, and his sweeper sees more action vs. righties. Even though the options become more limited depending on who is hitting, Legumina has demonstrated that each pitch can be successful.
Even with the way he utilizes his pitch mix depending on matchups, Legumina is above-average in the majors in chase rate (29.4%), whiff rate (25.3%) and strikeout rate (25.5%).
Legumina's walk-rate is the one outright poor aspect of his game, and the one that may have the biggest negative impact. His 11.8% walk-rate ranks in the eighth percentile of baseball. His other above-average numbers should allow him to work around that, but he's been one of the unluckiest relievers on the team.
Legumina's expected ERA (xERA) and expected batting average (xBA) are 3.49 and .221, respectively. Those numbers rank in the 69th and 80th percentile in the league, and are consistent with his pitch usage. With the exception of his fastball, every single pitch in Legumina's arsenal has a lower expected batting average than actual batting average.
His sweeper has a .208 xBA compared to .258 BA; His sinker a .162 xBA and .200 BA; and his changeup a .139 xBA compared to .190 BA.
At the end of the day, results matter more than anything. But Legumina's underlying numbers have been there, and he has shown impressive stuff the whole season.
If Legumina can cut down the walk-rate, it will eliminate some run-scoring opportunities for opposing teams and might allow his stuff to shine through.
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