Pirates' Mitch Keller injury shocker at trade deadline explains troublesome regression

Amid a frantic trade deadline that saw the Pittsburgh Pirates reshape their bullpen, the organization quietly revealed an injury development that may explain one of the most troubling individual regressions of its season.

The Pirates placed Mitch Keller on the 60-day injured list Monday with a right teres major muscle injury, ending the veteran right-hander’s season. Left-handed reliever Brandon Eisert was recalled from Triple-A Indianapolis in the corresponding move.

The timing of the announcement was startling. While attention was focused on Pittsburgh’s last-second additions of Luke Weaver, Lake Bachar and Kirby Yates, Keller’s disappointing year suddenly received important context. His struggles were not necessarily the product of a healthy pitcher simply losing effectiveness. At some point, he was attempting to pitch through a significant arm issue.

Keller finishes the season with a 6-8 record, a 5.29 ERA and a 1.37 WHIP across 22 starts. Those numbers were already concerning, but his recent performance had become increasingly difficult to explain. Over his final 15 outings, Keller recorded a 6.63 ERA and a 1.55 WHIP.

His last start against the Cincinnati Reds now looks even more alarming in retrospect. Keller surrendered seven earned runs on six hits and four walks while recording only six outs. It was one of the worst starts of his career and continued a prolonged stretch in which he looked nothing like the dependable rotation fixture the Pirates expected him to be.

The teres major injury doesn't erase Keller’s poor results, but it offers a plausible explanation for why his command, consistency and ability to finish pitches deteriorated so dramatically. Pitchers rarely disclose every physical issue while they are competing, and Keller repeatedly taking the ball may have obscured the severity of what he was dealing with.

Pittsburgh must now determine how long Keller had been compromised and whether the injury altered his mechanics enough to contribute to the extended slump. Those questions will matter as the Pirates evaluate his rehabilitation and plan their 2027 rotation.

Brutal Mitch Keller injury creates starting rotation opportunity for Carmen Mlodzinski

Carmen Mlodzinski is the most likely candidate to replace Keller in the rotation. Mlodzinski opened the season as a starter before being moved to the bullpen when Jared Jones returned from the injured list, a decision he made clear was not his preference.

The Pirates’ aggressive bullpen additions create enough depth to move Mlodzinski back into the role he wanted. It is hardly the way Pittsburgh hoped to create a rotation opening, but it gives him another opportunity to prove he belongs there.

Keller’s season ends as a statistical disappointment. The injury news, however, makes his regression more understandable — and raises uncomfortable questions about how long he was pitching at less than full strength.

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