Last Updated on December 16, 2020 by Luke Arkins

No unit on the Seattle Mariners’ roster improved more this year than its starting rotation. Could the same staff lead the Mariners to the postseason in 2021?

As preposterous as the notion may sound to some of you, I believe such a reality is achievable. What’s driving my seemingly over-optimistic assessment? Several factors favoring the Mariners heading into next season. Let’s discuss.

Quality Performers

Through the lens of xwOBA, we can get a sense of a pitcher’s ability to avoid quality contact and prevent base runners – two factors crucial to being successful. A particularly helpful aspect of xwOBA is defense and the official scorer have no influence.

In Seattle’s case, the rotation had a combined .308 xwOBA this year – ninth lowest in MLB and below the .314 MLB average starting pitchers. Not every outing was a success; there were clunkers. Nevertheless, manager Scott Servais received quality performances from his starting staff more often than the rotations of several postseason participants delivered this year.

A closer look reveals four Mariners facing at least 130 hitters as a starter had an xwOBA below the league average: Yusei Kikuchi, (.279), Marco Gonzales (.291), Nick Margevicius (.301), and Justus Sheffield (.303). Impressive considering most clubs with at least four starters meeting our 130-plus hitter/below league-average xwOBA criteria qualified for October baseball.

Number of SP’s with xwOBA Under MLB Avg
Five
Four
Three
Two
One
Zero
LAD*
SEA
LAA
ATL*
TOR*
DET
TBR*
HOU*
CHC*
SFG
CLE*
OAK*
WSN
SDP*
MIA*
MIL*
BAL
TEX
PHI
STL*
PIT
BOS
CIN*
ARI
KCR
COL
NYY*
NYM
MIN*
CWS*
MLB avg xwOBA for SP's = .314
* Made Postseason

It’s not surprising to see the Dodgers leading the pack with five starters – Clayton Kershaw (.263), Tony Gonsolin (.264), Julio Urías (.282), Walker Buehler (.283), and Dustin May (.304). All five return next year, plus 2012 Cy Young Award winner David Price is set to rejoin the team after opting out this year due to COVID concerns.

The Rays boasted Tyler Glasnow (.263), Charlie Morton (.293), Blake Snell (.295), and former Mariner prospect Ryan Yarbrough (.309). Complementing the starting staff was one of the best bullpens in baseball. We saw plenty of Tampa Bay’s dynamic and versatile group of relievers in the postseason. Perhaps we saw them too soon in Game 6 of the World Series. That’s a conversation for another day.

Cleveland was led by 2020 AL Cy Young Award winner Shane Bieber (.242), Zach Plesac (.274), Carlos Carrasco (.289), and Aaron Civale (.310). Just falling short of inclusion was top prospect Triston McKenzie (.289) with 127 hitter faced. The team was so deep in starting pitching, management was comfortable with trading Mike Clevinger to San Diego in late August.

In the Bronx, the Yankees rolled out Gerrit Cole (.262), J.A. Happ (.270), Jordan Montgomery (.292), and Masahiro Tanaka (.297). It’s worth noting rookie Deivi García just missed qualifying for our list with a .315 xwOBA. New York will be relying on 21-year-old to help to fill the void created by the potential free agent departures of Happ and Tanaka.

Two surprises- at least to me – were the Reds and Marlins. Both teams managed to qualify for the postseason with identical 31-29 records despite subpar run production. Only the Pirates and Rangers scored less than Cincinnati’s 4.05 runs/game. The Fish weren’t much better (4.38 runs/game). So how did these two clubs qualify for October baseball?

Quality starting pitching, of course.

The Reds boasted NL Cy Young Award winner Trevor Bauer (.219), Luis Castillo (.260), Tyler Mahle (.268), and Sonny Gray (.270). Supporting the rotation was a top-10 bullpen. Despite the 2020 success, the team faces the unenviable reality of losing Bauer to free agency.

Miami’s rotation was very young and very good. Leading the way, rookie Sixto Sánchez (262) followed by Pablo López (.270), Trevor Rogers (.278), and Sandy Alcantara (.298). All were 24-or-younger this year. Unlike Cincinnati, the Marlins’ bullpen was a weak spot for NL Manager of the Year Don Mattingly.

The two clubs not reaching the postseason despite having four pitchers meeting our criteria were the Phillies and Mariners. Philadelphia’s main rotation contributors were Zach Eflin (.270), Aaron Nola (.274), Zack Wheeler (.284), and Vince Velasquez (.295). The club also had a prolific offense that averaged over five runs scored/game. However, its bullpen was among the worst in baseball as was its defense.

Prospect Insider readers are well aware of Seattle’s shortcomings this year. Unlike the Phillies, defense was a strong suit with two Gold Glovers in the infield. However, the bullpen was wildly inconsistent and unreliable. Furthermore, the lineup delivered below-average production (4.23 runs scored/game and a 91 OPS+).

The 2020 seasons of the Phillies and Mariners demonstrate it takes more than good starting pitching to earn a playoff berth. Look no further than the Braves, Cubs, Padres, and Blue Jays for proof. Each team had either one or two pitchers meeting the 130-plus hitter/below league-average xwOBA criteria and still reached the postseason.

Still, I’d prefer being in the position of the Mariners over clubs without a solid core of starting pitchers to build around. As I’ve written before, premium, controllable starting pitching is the rarest of commodities in baseball.

Room For Growth

It’s plausible Gonzales, Kikuchi, Sheffield, and Margevicius are better next year. That’s an exciting proposition for the still-rebuilding Mariners.

Gonzales doesn’t fit into the mold of a prototypical staff ace, but the left-hander was top-20 in the majors in multiple categories including ERA, WHIP, BB%, SO/W, and innings pitched. Moreover, his .291 xwOBA was among the 30 lowest among MLB starters this year. There’s no reason to believe the 28-year-old Gonzaga alum can’t continue improving his mastery on the mound well into his thirties.

I recently wrote that advanced metrics suggest there’s a realistic path to greater success for Kikuchi. Yes, the 29-year-old’s conventional stats were underwhelming. But his team-leading .279 xwOBA is hard for me to ignore. The talent is there. All Kikuchi has to do is put it all together in 2021.

Just a season after the Mariners demoted him to Class-AA Arkansas due to control issues, Sheffield emerged as a cornerstone in the rotation. Considering he’s just 24-years-old, it’s reasonable to expect the best is yet to come for the southpaw.

Margevicius, who experienced a bumpy MLB debut with the Padres in 2019, appeared to find his comfort zone in Seattle this year. How he fits into the club’s long-term plans remains unknown. But the 24-year-old former Rider Bronc demonstrated during his 2020 audition he possesses the ability to deliver quality from the back of the rotation.

Potential Help From Within

There are several young arms in the organization, who may prove capable of complementing or even supplanting the quartet we’ve discussing. The most notable names are Justin Dunn, Ljay Newsome, and Logan Gilbert. For now though, they remain unknown commodities with potential heading into next season.

Dunn’s 4.34 ERA during 10 starts this year doesn’t look that bad for a rookie. Moreover, opponents hit .189 against him, which was the eleventh lowest AVG among starters this year. However, Statcast paints a different picture. The Boston College product rated poorly across the board, particularly in elements affecting xwOBA – exit velocity, plus strikeout, walk, and barrel percentages.

Justin Dunn’s 2020 Statcast Page

Still, Dunn will be entering his age-25 season and may simply need more time to blossom in the majors. After all, he never pitched above AA before joining the Mariners as a September call-up in 2019. That said; it’s possible the team eventually transitions the right-hander to the bullpen.

It’s worth noting Jason A. Churchill suggested this possibility in his 2020 Prospect Rankings. Churchill commented Dunn’s fastball velocity could tick up to the 95-99-MPH range as a reliever, while his slider may rival Edwin Díaz’s.

As Corey Brock of the Athletic noted in January, Newsome benefited from the Mariners’ “Gas Camp” prior to the 2019 season. The right-hander’s fastball velocity prior to attending averaged 88-MPH. In 15 innings with Seattle this year, his velo was at 91.4-MPH. The Maryland native isn’t a “swing and miss” type, although he doesn’t surrender free passes often. In 2019, his 2.7-percent walk rate was lowest among 436 minor leaguers throwing 100-plus innings. With Seattle, he walked one of 68 batters faced.

Gilbert is the organization’s top pitching prospect and probably would’ve debuted sometime during the 2020 season, if the pandemic shutdown minor-league baseball this year. Perhaps the 23-year-old joins the Mariners next season and makes an impact as Sánchez did with the Marlins. Then again, Gilbert could initially struggle facing big league hitters similar to the way Sheffield did.

Another potential contributor to the rotation could be Chris Flexen, who the Mariners reportedly signed to a two-year deal last week. In 68 innings spread over three seasons with the Mets, Flexen walked more hitters (54) than he struck out (49). However, the 25-year-old started games in Korea this year striking out 132 and walking just 30 in 116.2 innings.

More Postseason Opportunities

MLB commissioner Rob Manfred prefers continuing an expanded postseason format in 2021. Previous comments from Manfred suggest something less than the 16 teams making the playoffs in 2020, but more than the usual 10 reaching October prior this year. The logical outcome is either a 12 or 14-team bracket.

Assuming Manfred gets his way, there will be more paths leading to the postseason in 2021 than prior to the pandemic. This bodes well for a club like the Mariners that’s trying to pivot from rebuild-mode to relevance.

Looking To 2021

Despite the rosy picture I’ve been painting, there are potential landmines that could stall the Mariners’ postseason aspirations next year.

Obviously, run production must improve. More importantly, GM Jerry Dipoto needs to acquire quality late-inning relief arms capable of depressurizing the bullpen for the team’s younger relievers.

Regression by Kikuchi, Sheffield, or Margevicius is a potential obstacle. So is Gilbert stumbling out of the gate. One way Dipoto could mitigate risk would be adding an established starter. Specifically, a postseason-tested veteran capable of stabilizing a staff comprised of mostly young or inexperienced arms. Not long ago, we discussed eight potential candidates Dipoto could consider.

Assuming the Mariners confront these issues head on, the rotation can lead a Seattle march back to the postseason for the first time since 2001. Perhaps vying for the AL West division title, as Dipoto has suggested, would be a bridge too far. But a Wild Card berth would be fine at this point.

Wouldn’t you agree?

My Oh My….

Image courtesy of Stephen Brashear / AP Images
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