Now that we’ve covered all of the position players for the Mariners in 2020, it’s time to look at the backbone of this team’s rebuild: the starting pitching. The Mariners took a different approach this year, opting to keep a six-man rotation throughout the entirety of the season. While the M’s claim the system kept pitchers healthy and argue that it could be a feature they keep for the 2021 campaign, it also allowed them to get deeper looks at potential pillars of a future winning team. For the most part, the tactic worked. The team used far fewer arms this year than they have in years past.
2020 Mariners Starting Pitchers
Marco Gonzales continued on as Steady Eddie for the M’s this season. He started on Opening Day and never missed a turn throughout the season. In fact, Gonzales put together his best stretch as a Mariner — albeit over just 11 starts. He posted career bests in ERA and FIP as well as in peripheral stats like K/9 (8.27) and BB/9 (0.90). His refined command earned him the second-best BB/9 in the majors, trailing only Kyle Hendricks of the Cubs (0.89). Marco is what he is, and what he is is a very valuable and stable arm the M’s will be able to rely on as they fill in the pieces around him. He allayed some of the worrisome contact numbers from 2019 that didn’t lead to consequences, yielding an average exit velo well below league-average and a xwOBA (.291) 30 points lower than league average. His four-year, $30M extension kicks in next season and it’s beginning to look like a steal for Seattle. He’s likely to start Opening Day in 2021, barring some splashy signing or trade.
But the starter who took the biggest leap this year was Justus Sheffield. The left-hander the M’s acquired in the James Paxton trade altered his repertoire entering the season, completely abandoning his four-seam fastball in favor of a new sinker. He saw excellent results overall, dropping his BB/9 from 4.50 in 2019 to 3.25. He allowed just two homers all season and embraced his strengths as a sinkerball pitcher. Everything he threw dropped, with his slider remaining solid and his changeup continuing to develop into a sharp dropping offering. Given that he’s a part of the Rookie of the Year discussion, he’s pretty much guaranteed a spot in next year’s rotation. Still, it would be nice to see another step forward from his sinker if he’s going to keep using it as much as he is (47.4%), given that it allowed a .353 xwOBA. It certainly has potential to become a plus offering thanks to his above-average sinking vertical movement on the pitch. But it has its drawbacks. For starters, he’ll have to learn to spot it a lot better. He got strikes on the pitch just 53% of the time, and if it’s going to be his go-to offering, he’ll have to become more confident in locating it in the zone. Whether that means working in more four-seamers or sharpening his sinker can go either way.
Conversely, 2020 was another disappointment for Yusei Kikuchi. The promising left-hander had pretty poor results for the second season in a row, and at some point soon he’s going to have to produce. There’s some good news hidden underneath the hood, like his gaining 2.5mph on average on his fastball. His FIP was much better too, partially because he only allowed three home runs all season. His slider turned into a strong secondary offering for him this season, and he’s certainly shown flashes — like when he struck out nine over six shutout innings against Oakland. While I fully expect Kikuchi to be given another chance in 2021, he’s running out of opportunities with the guys Seattle has coming up the pipe. His unique contract means he’ll need to put together some results to match his stuff in 2021 or the Mariners may need to reevaluate.
While fellow top organizational prospect Sheffield has cemented his role in the starting rotation, that job is far from guaranteed for Justin Dunn. The secondary headliner from the Robinson Cano/Edwin Diaz deal averaged just 91.2mph on his four-seamer this year after being more of a 93-95 guy in the Mets’ system. There are a few reasons to believe he’s more of a reliever long-term, from his diminished velocity in long stints to his hefty righty-lefty splits (.362 wOBA vL, .278 wOBA vR) to his lack of a true third offering after his fastball and slider. He’ll need to carve out a strong third pitch and vastly improve the command on his heater to stay in the rotation. It’s a tough ask, but the M’s spent enough capital to get him — and were reportedly super high on him coming out of the draft — that I think they give him another go at it in 2020.
Nick Margevicius was a pleasant surprise for the team in 2020. After being claimed on waivers from the Padres in January, Margevicius impressed enough in his three relief stints to earn a rotation spot in August. The 24-year-old turned into a reliable innings-eater for the squad, tossing at least five innings in five of his last six starts. He turned his slider and curveball into very capable offerings in 2020, earning him a membership card to the Crafty Lefties Club. His status as a starter is wholly reliant on what the M’s do this offseason, and whether they choose to keep the six-man staff. If nothing else, he can be kept on the roster as a reliever with the option to be a plug-and-play guy if injuries arise.
Taijuan Walker, how we miss you so. The triumphant return of the former top prospect turned out to be a pretty harmonious reunion. Walker more than delivered on his one-year, $2M bargain bin contract, even if his FIP suggests that he got a little lucky in Seattle. The Mariners flipped him at the deadline for young outfield prospect Alberto Rodriguez of Toronto, where he helped propel the Blue Jays to a playoff spot by allowing two earned runs or fewer in every outing. Walker is now a free agent once more. Perhaps another reunion is on the horizon. If not, it was fun while it lasted.
One of the biggest victories for the Mariners’ player development on the pitching side under Jerry Dipoto has been Ljay Newsome. The former 26th rounder made his MLB debut this season after slowly making his way up the ladder, and sans one blow-up outing against San Francisco, held his own. I expect him to be given a shot for a rotation spot in 2020, but it certainly won’t be guaranteed to him. Notably, we’ll need to see him get stretched out; he hasn’t thrown more than 90 pitches in an outing since July 21, 2019 when he was in Double-A Arkansas. For more on what kind of arm he can be for Seattle, I recommend reading Mikey Ajeto’s deep dive on the right-hander. He’ll likely start 2021 in Tacoma, but be one of the first players up in case of injury.
Kendall Graveman amassed something of a cult following coming into the 2020 season, with Mikey hyping him up pretty significantly prior to the start of the season thanks to the right-hander’s searing velocity. He certainly got me on board, considering I foolishly predicted that Graveman would lead M’s starters in ERA this season. Unfortunately, it was not to be. Graveman suffered a neck injury in his second start of the season, sidelining him for a month. When the M’s brought him back, it was strictly as a reliever. After allowing eight earned runs in 8.2 innings as a starter, Graveman allowed just four in 10 innings out of the bullpen. If he stays with the team in 2020, it’ll probably be as a fairly interesting bullpen arm.
That brings us to the two fill-in arms the M’s used in 2020: Jimmy Yacabonis and Nestor Cortes. The most memorable thing either of them did might have been the home run that Cortes gave up to Albert Pujols in late July. Both of them have elected free agency and aren’t likely to return to the organization.
With the upcoming stable of top-flight pitching prospects, the remaining players will have to duke it out for the shrinking number of available spots in the team’s rotation. Gonzales and Sheffield are the two you can write in with a sharpie, and Kikuchi will almost certainly join them. Beyond that, everyone will be auditioning for a spot in spring training. Perhaps the Mariners will even make it more interesting by bringing in one Marcus Stroman. We can all hope.