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Miami Marlins pitcher Sean Guenther (66) stands in the dugout before the game against the Washington Nationals at loanDepot Park

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2021 Marlins Season Review: Sean Guenther

Evaluating the ups and downs of Sean Guenther’s rookie year.

Rhona Wise-USA TODAY Sports

Sean Guenther allowed a lot of runs in not a lot of innings during his first taste of the majors, but there is more to his story.

2021 Timeline

  • June 8: promoted from Double-A Pensacola to Triple-A Jacksonville
  • August 1: contract selected from Jacksonville
  • August 4: made MLB debut vs. Mets
  • August 9: optioned to Jacksonville
  • August 14: recalled from Jacksonville
  • October 3: placed on 10-day injured list
  • October 5: activated from IL

By The Numbers

2021 Marlins pitching stats FanGraphs

Guenther is among the best control artists in Marlins minor league history. FanGraphs MiLB leaderboards date back to 2006—during that span, his 3.4% career walk rate is the lowest for any of the organization’s pitchers with a minimum of 200 innings. He threw only eight wild pitches as a farmhand.

He stayed true to his track record with Double-A Pensacola and Triple-A Jacksonville. Most notably on May 22, he racked up eight strikeouts in three perfect innings vs. the Rocket City Trash Pandas. That came in the midst of a month-long scoreless streak.

The 25-year-old left-hander received a promotion to Miami shortly after the trade deadline passed. However, it was a bumpy transition.

Guenther threw 63% of his pitches for strikes with the Marlins, compared to 69% in the minors. He got to 0-2 counts in just 19.4% of his major league plate appearances (MLB average is 26.4%). Deployed exclusively in relief, he allowed baserunners in 12 of his 14 games.

No doubt, Guenther was victimized by some bad luck. He surrendered a sky-high .411 batting average on ball in play despite relatively normal opponents’ quality of contact. But he was at the mercy of the BABIP gods because of his lack of swing-and-miss. None of his individual pitches—four-seam fastball, slider or changeup—induced a whiff rate above 25%. He was especially helpless against fellow lefties, allowing a .447/.512/.579 slash line with only three strikeouts in 44 plate appearances.

Listed at 5-foot-11, Guenther was the shortest pitcher to spend significant time on the Marlins active roster (journeymen Austin Pruitt and Taylor Williams excluded).

The sample size is laughably small, but Guenther tossed 4 23 scoreless innings when paired with Sandy León and Jorge Alfaro. All of his struggles came when following the lead of younger catchers (Nick Fortes, Payton Henry and Alex Jackson).


Will Sean Guenther Be Back in 2022?

It’s highly unlikely that Guenther will stick on the Marlins 40-man roster throughout the offseason. Their 40-man is full as of this writing with several glaring needs yet to be addressed. Being a relief-only option with ordinary raw stuff and no MLB success on his résumé makes him expendable.

Also working against Guenther: he was drafted by the Marlins in 2017, the summer before new ownership came in. The current decision-makers aren’t invested in his success to the same extent as a more recently acquired player.

There is a solid chance that Guenther would clear waivers if designated for assignment. The Marlins could then outright him to the minors. From there, he’d attempt to earn his way back up to the highest level.

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