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LL’s Top 50 Mariners Prospects: 50-47

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Two infielders and two righty pitchers kick off the list

MLB: Seattle Mariners-Media Day Mark J. Rebilas-USA TODAY Sports

Today we kick off the countdown of the top 50 prospects in the Mariners organization with the first four on our list: a pair of infielders and two right-handed pitchers. Or maybe: a pair of infielders, a right-handed pitcher, and a two-way player? It’s too early to tell for 2018 draftee Joey O’Brien.

After opening his professional career with a trio of impressive campaigns from 2015-2017 that saw him post wRC+’s of 129, 124, and 151, Rosa failed to get the bat going last season, posting a 72 wRC+ in his first extended taste of Clinton. The speedster posted BABIPs north of .350 in each of his first three seasons but put up a mark of just .283 in an injury-plagued 2018 season during which he also posted a career high FB% of 39.3%. The 29.5% OPP% he posted last year bested his previous career high by nearly 5% while he pulled the ball 6.1% of the time less than ever before and more than 14% less often than in 2017. A switch-hitter, he’s fared better from the left side of the plate throughout his young career. Rosa is aggressive on the bases, but will have to clean up the amount of times he’s caught before speed can be considered one of his tools. -BT

A four-year starter at Oklahoma State, Donnie Walton forewent signing each of the first two times he was drafted before inking a deal with the Mariners after closing out his career with the Cowboys. He’s showed off good bat-to-ball skills throughout his career, never exceeding an 18.0% strikeout rate and consistently hovering around a 10% walk rate. After suffering an injury that cut short his 2017 season, Walton put up a 131 wRC+ through 57 games at High-A last season in his second time through the level, and was rewarded by moving up to Arkansas to close out the year, where he struggled to an 83 wRC+ through 62 games. He’ll need to replicate what he did in 2018--post big time numbers while repeating a level--or he’ll be at great risk of falling far behind the development curve considering the advanced age at which he entered pro ball. -BT

It’s entirely possible that Ljay Newsome has already seen the peak of his professional career. After winning the C-the-Z contest two seasons ago, Newsome earned a spring training invite despite never pitching above Clinton or appearing on the team’s top prospect lists. Once there, he earned the respect of the club with a quiet, professional demeanor and threw three innings without allowing a run, striking out two. Newsome’s elite command and ability to keep his offerings down in the zone have served him well at the Mariners’ lower levels, but his stat line jumped up pitching in more difficult and hitter-friendly Modesto in 2018. He’ll look to return to his 2017 success in 2019, likely while repeating the level in Modesto. - TC

With the shadow of Shohei Ohtani Kaleb Cowart cast across the entire league, Joey O’Brien looks like the best bet at a two-way talent in the Mariners’ minor league system. Tragically, he’ll likely be limited to pitching at this stage in his career. Raised in Japan, O’Brien offers an “Iwakuma-like” motion and a similar four-seam/curveball/splitter arsenal. Despite success in his time at a high-level JUCO, the lack of information or track record on O’Brien makes him a longshot for MLB impact, he’s also easily the likeliest of this group to emerge as a big leaguer one day. A 91-96 mph fastball and well-regarded control is a good place to start, and with his size and skillset, starting is exactly what he’ll have a chance to do. The dearth of alternative SP options makes O’Brien worth watching, raw as he may be. ~ JT