Mariners Top 30 Prospects: A 2021 Midseason Ranking

#20: Jonatan Clase

Jonatan Clase is a lightning-fast outfielder signed out of the Dominican Republic in 2018. The short-statured CF has stolen 16 bases without being caught all year and appears to be learning how to switch hit. Clase has an incredibly strong work ethic and is obsessed with improving both his body and skills to maximize his potential. The 19 year old is off to a fine start for his 2021 season and should only continue to improve.

#19: Isaiah Campbell

Vying to be the first Portugese MLB player since 1875, Isaiah Campbell is a 6’4″ RHP drafted out of Arkansas in 2019. The big right-hander was an invitee to the “Summer Camp” instructional training over the 2020 pandemic and was able to improve alongside other top prospects. Currently on the injured list, Campbell has shown great success in High A Everett when healthy.

Campbell expects to move quickly through the system upon his return from the IL and could be a contributor to the big league squad as soon as the end of beginning of the 2023 season.

#18: Alberto Rodriguez

The compensation for last years Taijuan Walker trade, Alberto Rodriguez is an outfielder hailing from the same town as Noelvi Marte, one of the Mariner’s premiere prospects. While he has been longtime friends with Noelvi, he can bring much more to the table than mere companionship. Currently slashing .286/.379/.475, Rodriguez has coupled a very promising bat with solid defense in the corner outfield positions. Just 20 years of age, Rodriguez has a bright future ahead of him.

#17: Kaden Polcovich

Kaden Polcovich was drafted in the third round of the 2020 draft out of Oklahoma State University. The epitome of a super utility player, Polcovich can play all over the diamond with solid skills in both the infield and the outfield.

After an exceptional start in High A Everett with an OPS of .920, Polcovich has struggled mightily after the jump to Double A Arkansas. Despite his struggles, the defensive utility and flashes of offensive upside remain key factors into his development path and leave plenty of room for growth for the Oklahoman.

#16: Juan Then

Juan Then is a RHP acquired in the Edwin Encarnacion trade in 2019. A fireballing right-hander, Then likely projects to be a back-end reliever at the major league level. While there is still a chance he could start, his struggles this year may push the Mariners to shift his development to operate as a multi-inning reliever rather than a pure starter.

Despite the lack of results this year Then possesses the tools to become a successful major league pitcher. Already on the 40-man roster, expect to see Juan Then in the big league bullpen sooner rather than later.

#15: Edwin Arroyo

The Mariner’s second round draft pick in the 2021 draft, Edwin Arroyo is a SS out of Puerto Rico. With a cannon arm and premiere defensive range, there is no doubt the young Puerto Rican can stick at SS. One of the youngest players selected in this years draft, the 17 year old will benefit greatly from a guided development program.

The bat lags behind the glove right now, however the hit tool has shown flashes of serious upside. While you likely won’t see him in the big leagues any time soon, keep a close watch on Arroyo as his career goes on.

#14: Milkar Perez

An international signing out of Nicaragua in 2018, Perez has shown a tremendous ability to get on base in his time as a professional. Currently sporting a .474 OBP this year, the 19-year-old third baseman still has plenty of time to let his body mature and fill out his 5’11 frame. Should more power come from Perez’s bat, Perez will fly up scouting boards and has the chance to grow into a top 10 prospect in an already strong Seattle system.

#13: Andres Munoz

While technically not considered a prospect by definition, we decided to include Munoz in our list considering he has only 23 major league innings and is still just 22 years old. Munoz is the prototype for a high-leverage reliever. With a 100+ MPH fastball and a devastating slider at his disposal, Munoz has already struck out 30 batters in his short stint as a big leaguer. Currently on the cusp of his recovery from Tommy John surgery, look for Munoz to be a major contributor to the Mariner’s 2022 bullpen.

#12: Adam Macko

A Slovakian LHP that was drafted out of a Canadian high school in the seventh round? Adam Macko’s progression to professional baseball has been anything but normal. Nevertheless, the 20-year-old starter has shown immense stuff from the left side.

Armed with a low-to-mid 90’s fastball and two devastating breaking balls, Macko has struck out 56 batters in just 33.1 innings. I am personally very high on Macko’s abilities and believe he has a real shot at being a serious contributor at the major league level. He has significant breakout potential.

#11: Connor Phillips

Just missing the top 10, Connor Phillips was a Compensation Round B pick out of McClennan CC in Texas. Similar to his Modesto teammate Adam Macko, Phillips has shown a proficiency for striking people out. His 82 K’s in 61 innings have been a serious bright spot in Phillips’ young career.

While he needs to limit his walks, the stuff is electric and there is little reason to believe the exceptional pitching development team Seattle has in place can’t help him alleviate that issue. If Phillips can limit the walks, the stuff will carry him to a successful major league career as a starting pitcher.