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Sean Guenther: Marlin on the Rise

Do you have the GUENshow?

For the 2016-17 offseason, we counted down the Top 100 all-time Marlins. This offseason, we will instead cast our eyes ahead. I’ll be outlining the Top 100 Marlins prospects, as chosen by you on the listing.

Sean Guenther, Miami’s seventh round pick in 2017, was born on December 29th, 1995. A 5’11”, 185 lb. left-handed pitcher, he played for the Notre Dame Fighting Irish in college.

Guenther started 12 times over three seasons at Notre Dame, coming on in relief 54 times. In spite of his time on the mound being so heavily weighted towards relieving, the Marlins have him pegged as a future starter, and put him on that track after his selection. For the Irish, he posted a 6-14 record, a 3.51 ERA, a 1.34 WHIP, and 153 whiffs in 182 frames.

After Guenther’s selection, 209th off the board this past June, the Marlins assigned him to the GCL Marlins. After a scoreless relief appearance on July 2nd, he ended up making three rotational starts. In 10 innings over the three starts, he surrendered just five hits and one run, striking out nine and walking zero. On July 11th, he struck out four over three walkless and hitless innings in a 13-3 Marlins win against the GCL Mets. After 11 innings at the rookie level, Guenther, who owned a 0.82 ERA, was promoted to the Muckdogs.

Guenther uses a compact delivery and holds runners on well. Once he kicks his leg, his explosion towards home is quick and powerful. For a batter, this makes it difficult to read the ball coming out of his hand. He mechanics are repeated with regularity regardless of which pitch he’s throwing, making his off speed stuff more deceptive. - Michael Napoles, at

Guenther has fastball that hovers between 88 and 92, peaking around 93 MPH. Although he doesn’t yet have a clear secondary pitch, he reportedly has a “deep assortment of offspeed stuff.” (h/t to Rob Ozga over at

With low-A Batavia, Guenther made nine rotational starts, racking up a 1-4 record, a 3.83 ERA, a 1.175 WHIP, and a .270 opposing batting average. His best stretch of the season was from August 1st through 20th, when he went 1-0 and struck out 17 in 19 innings while giving up just three runs and a single walk.

In total, Guenther held opposing batters to a .241/.273/.347 slash line, while walking five batters to 44 whiffs in 51 innings. Maybe most impressive was his performance on the road, in which he put up a 0.609 WHIP in 23 innings of work.

Gunther’s already pretty solid, and the Marlins should probably send him to the Greensboro Grasshoppers to start the 2018 campaign.