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LL’s top Mariners prospects 2020: 10 and 9

Two pitchers with great expectations still ahead of them.

Cincinnati Reds v Seattle Mariners Photo by Norm Hall/Getty Images

We have trekked from the Dominican Republic to Arizona to West Virginia to Modesto to Arkansas to Tacoma as we’ve looked at the talent populating the Mariners system. Some of the lights have been more distant or fainter than others, but as we round into the Top 10 we come to lights that are brighter, closer, or, excitingly, both.

From here on out we’ll be profiling two players a day with slightly more in-depth write-ups than our previous forty. Remember if you’ve missed any of the prior installations, you can catch up on numbers 50-11 and the introduction to the series in the main hub here.

10. LHP Justus Sheffield

A zero has been added behind Sheffield’s name in the rankings from his place on many lists a year ago. In between club lunches with his “prospect fatigue” brethren Lucas Giolito and Jurickson Profar, Sheffield spent this winter training with a certainty ahead of him previously unspoken: he will have a spot in the rotation for the 2020 Mariners, and he will have it all year. It’s a level of security that hopefully translates to better consistency than Sheffield showed in 2019, traveling (no pun intended) from AAA to MLB to AAA to AA and finally MLB for good.

Sheffield’s repertoire has relied on three pitches, primarily focused on a sinking four-seam fastball that works 92-95, topping at 96. He misses bats with aplomb thanks to a brilliant hard slider that tunnels nicely with his other pitches but has exceptional late multi-plane break, making it challenging for right-handed hitters and devastating to lefties. His changeup lacks a traditional velocity gap, coming in firmer than preferable, but its movement is reasonable and improved command and comfort with it should help him keep righties at bay - vital for sticking in the rotation through multiple times through the rotation.

Notably, Sheffield has recently adopted a two-seam grip on his fastball, with great success in his first outing using it exclusively, offering an interesting possibility going forward. Despite its league-average velocity, Sheffield’s fastball has been his least-successful pitch in MLB. Its low-spin properties make it functionally a sinker, which works at the bottom of the zone, but can be detrimental at the top of the zone, and may even reduce Sheffield’s command of the pitch. If the two-seam, which naturally is meant to sink and run, can combine with Sheffield’s natural low spin, it could make for a more effective pitch and help solidify Sheffield as a groundball starter who can work more efficiently.

This season is vital for Sheffield all the same, as his size, lack of command at times, and underdeveloped changeup have long spelled reliever risk. This year will be crucial in Sheffield’s chances to prove that fear wrong and take the ball every five games.

9. RHP Justin Dunn

With big spending impending for the Mariners, Dunn will have all of 2020 and likely at least a portion of 2021 to prove he is capable of handling a big league rotation spot. If not, the stuff could play quite nicely in the back end of a bullpen. Dunn’s athleticism suggests there’s more in the tank should he choose to open it up with the fastball. At worst, he’s could be an 8th or 9th inning guy that pumps 97 into the zone with a plus slider. Sound familiar?

As a starting pitcher, the former Boston College standout utilizes a mid-90s fastball and sharp slider to keep hitters off balance. As of late he’s mixed in a changeup that has proven valuable, especially the second time through a lineup. The key for Dunn in 2020 will simply be to throw strikes. The stuff is ticking up as his development has progressed, and the fastball has shown more late life, exhibiting well-above average spin rates. Dunn tunnels his three-pitch mix well, it’s just a matter of throwing them over the plate. If he can prove the secondaries can land for strikes consistently, allowing him to get ahead of hitters, he may meet his back end rotation ceiling.

Dunn got opposing hitters to hack at 45 of his pitches last season in his abbreviated visit to Seattle. Interestingly, not one of those pitches was considered barreled up. It speaks toward the stuff he naturally possesses.

The fastball? Plus. The slider? Plus. The hair? Plus-Plus. The swag. Elite. It’s hard not to root for a guy like Dunn, and he’ll give Mariners fans plenty of opportunities to do just that in 2020. It’ll ultimately be up to him as to whether he takes the mound before or after beers stopped being served at T-Mobile park each night. - JD