Marlins Prospects: Welcome to Sean Guenther’s Guenshow

Sean Guenther is another under the radar prospect in the Marlins system.

Sean Guenther, a five-foot-11 left handed pitcher from Atlanta, GA, was taken by the Marlins in the seventh round of the 2017 MLB Amateur Entry Draft. In three seasons with the Notre Dame Fighting Irish, he was 6-14 with a 3.51 ERA and 153 strikeouts in 182 1/3 innings.

Despite concerns about Guenther’s height and middling 1.33 collegiate WHIP, Miami obviously saw something they liked. In his first four professional games, including three starts for the Rookie-level GCL Marlins in the Gulf Coast League, he allowed five hits in 11 innings, with 11 strikeouts, one run allowed, and a 0.545 WHIP.

Just two weeks into his pro career, Guenther was pushed up a level to the Batavia Muckdogs, the Marlins Short-season-A New York-Penn League affiliate. He struck out 33 batters in 40 innings, going 1-4 with a 3.83 ERA over nine starts. Although he allowed 43 hits, he kept his WHIP to a tidy 1.18 by issuing only four walks during that time.

2018 would start with Guenther producing underwhelming results with the High-A Jupiter Hammerheads in the Florida State League. In seven starts, he was 0-1 with a 4.83 ERA and 48 hits allowed in 31 2/3 innings. Despite those struggles, he only walked three, continuing to demonstrate his control proficiency.

Pushed down a level midway through the season to the Greensboro Grasshoppers in the Single-A South Atlantic League, Guenther went 4-3 with a 4.45 ERA in 13 appearances, including eight starts. He walked five and struck out 40 in 54 2/3 innings.

As encouraging as Guenther’s control was over his first two professional seasons, he was still getting hit pretty hard. That, too, changed in 2019.

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Guenther began 2019 still ensconced at the Marlins Single-A level, although the venue had changed to the Midwest League and the team to the Clinton LumberKings. Used almost exclusively in relief at this point, Guenther started once and came out of the bullpen 11 times, going 2-2 with a 1.24 ERA. He struck out 28 in 29 innings and held the opposition to 25 hits for a 1.21 WHIP.

Encouraged once more, Miami promoted Guenther back to the Hammerheads. In his second look at the higher level, he produced his best results yet, going 3-1 with a 2.55 ERA, 44 whiffs in 42 1/3 innings, and walking only six for a microscopic 0.87 WHIP.

Guenther, who turns 24-years-old today, currently resides in the Marlins “second wave,” and should surface for the team sometime in 2021. Look for him to begin the 2020 campaign with the Double-A Jacksonville Jumbo Shrimp, in the Southern League.