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Fans of the Seattle Mariners became very familiar with the band of unheralded relievers that propelled the team into postseason contention this year. Perhaps a few east coast pundits even took notice of Seattle’s bullpen along the way.

Names like Paul Sewald, Drew Steckenrider, Diego Castillo, Casey Sadler, and Anthony Misiewicz anchored a Mariners bullpen comprised mostly of youngsters and journeymen that was better than good. They were among baseball’s best. 

Sure, the Rafael Montero and Keynan Middleton experiments did not pan out, nor did Rule 5 draftee Will Vest. Trading key relievers Kendall Graveman and JT Chargois in July certainly did nothing to improve clubhouse or fan base morale. But in the end, the bullpen provided manager Scott Servais with a distinct tactical advantage over opposing clubs throughout the season.

Whether you prefer conventional statistics or new-age metrics, Seattle’s bullpen was significantly better than the 2020 version that was arguably one of the worst in MLB. In fact, it was top-10 in multiple statistical categories.

M’s 2021 Bullpen vs 2020 Version

As you might expect, several surprising relievers blossomed for the Mariners. Players who were revelations to the team, its fan base, and the baseball establishment. None was bigger than Sewald.

Sewald went from a Mets castoff in 2020 to a high-leverage arm in Seattle a year later. Only two pitchers with 60-plus innings this season bested his 39.4% strikeout rate – Jacob deGrom (45.1%) and Liam Hendriks (42.3%). Impressive for a reliever with a 23.5% strikeout rate in four previous seasons.

Another good news story was Sadler, a waiver claim arriving in the Emerald City from the Cubs in September 2020.

Sadler did not allow a run in his final 29 appearances, which was the longest streak of its kind this season. The basis for such success was the 31-year-old’s knack for avoiding quality contact, which was reflected in a .242 xwOBA that was ninth best in the majors among relievers facing at least 100 hitters in 2021.

Expected Weighted On-Base Average (xwOBA) uses quality of contact (exit velocity and launch angle) to determine what should have happened to batted balls. A key advantage to xwOBA is defense (good or bad) does not influence it. This gives us a truer sense of how a hitter or pitcher is performing. MLB league-average xwOBA = .314

The third prominent member of Seattle’s posse of misfit relievers was Steckenrider. The 30-year-old spent three seasons with Miami, but did not appear in a game with the team in 2020. This year, he led Mariners relievers with 67.2 innings and was Servais’ most called upon arm in the ninth inning (24 games). Sewald was second with 18 appearances.

Other relievers contributing to the Mariners’ late postseason push included Joe Smith, Yohan Ramirez, Matt Andriese, Erik Swanson, Sean Doolittle, Justus Sheffield, and rookies Wyatt Mills and Andrés Muñoz. Together, they helped form one of the best bullpens in franchise history.


Better Than Most

Okay. I am not trying to persuade anyone into believing the 2021 Mariners’ bullpen was the “best ever” in team history. Comparing contemporary bullpens to those from bygone eras can be challenging.

Reliever utilization has drastically changed since the Mariners first debuted in 1977. Particularly with an increased emphasis being placed on specialized relievers since the team’s inaugural season and the recent trend of “bullpening” across MLB. Still, this year’s group does compare well to previous editions.

2021 Bullpen Ranks Well In M's Franchise History

The 2021 bullpen did not have stars such as Edwin Díaz, Fernando Rodney, Kazuhiro Sasaki, J.J. Putz, or Bobby Ayala at the ready to close out games. Yet, the 7.0 fWAR accrued by its potpourri of relief arms set a franchise record. This seems good and special.

I was kidding about Bobby Ayala. That was a test to see if you were paying attention.

So, how did the Mariners reap so much value from a bullpen short on recognizable names or established performers?

Success Under Duress

Simple. Servais maximized his bullpen’s effectiveness by masterfully juggling relievers to setup the best matchups, regardless of inning. This helps explain why Seattle was the only team with three relievers recording 10 or more saves in 2021 – Graveman, Sewald, and Steckenrider. Eighteen clubs had one or none.

Since the Mariners’ skipper did not use traditional thinking when deploying relievers, we should not rely on conventional statistics to discuss the impact of his bullpen management. A better option would be a metric that attempts to quantify a player’s influence on their team’s success.

Win Probability Added (WPA) credits or debits pitchers and hitters based on how the outcome of a plate appearance affects the chances of their team winning. For example, a late-inning home run in a close game earns a hitter more credit and the pitcher a larger debit than a homer in the first inning or in a blowout.

Using WPA is particularly helpful when discussing relief pitching. The best relievers are most often entrusted with safeguarding their team’s interests in the most crucial moments of a game. It is why elite relief arms can have a higher WPA than most starters. Conversely, less reliable or inexperienced relievers will have a low or negative WPA.

The Mariners boasted three pitchers with a top-20 WPA among relievers – Graveman, Steckenrider, and Sewald. Two of them landed in the top-10.

Top Reliever WPA In 2021
Josh HaderBrewers4.862
Jordan RomanoBlue Jays3.732
Raisel IglesiasAngels3.701
Kendall GravemanMariners/Astros3.350
Ian KennedyRangers/Phillies3.305
Jonathan LoáisigaYankees3.259
Tyler RogersGiants3.168
Drew SteckenriderMariners3.158
Ryan PresslyAstros3.089
Mark MelanconPadres3.015

Essentially, Servais skillfully placed relievers in the best position to succeed and they delivered positive results much more often than not. As a result, Seattle’s relief arms combined for a 7.71 WPA, which was fourth highest in the majors. The three clubs ahead of the Mariners owned the best win-loss records in baseball – the Giants, Dodgers, and Rays. 

Sounds like Manager of the Year material to me.

Can They Do It Again?

The main relievers with the Mariners at season’s end remain under club control for 2022 with the exception of Smith. That sounds like good news. But can the same cast of characters repeat its success next year?

Ah, the question on everyone’s mind.

Reliever volatility is a term often bandied about for good reason. Predicting how a reliever, or a bullpen, will perform from one year to the next can be problematic. In the Mariners’ case, a few issues are worth of mention as the offseason begins. Most notably, the team’s breakout performer.

As wonderful as Sewald was this season, there were noteworthy blemishes on the stat sheet. The right-hander was adept at missing bats. But when opponents did make contact, it was the damaging type more often than preferred. Among 306 relief pitchers allowing at least 100 batted balls this season, Sewald’s 12.6% barrel rate was eleventh highest.

Barrels are batted balls with the ideal blend of launch angle and exit velocity. In 2021, MLB hitters had a .772 AVG and 2.591 SLG on barreled balls. Also, 84% of all home runs were barrels.

In the same vein, Sewald allowed six home runs in September after surrendering four dingers in his four previous months. Perhaps fatigue spurred late-season longball struggles. The San Diego alum pitched just six innings with New York last year. In 2021, he logged over 11 times that much with Seattle and Class-AAA Tacoma, including an AL-leading 32.1 frames following the MLB trade deadline.

Misiewicz also struggled with well-struck balls. Opponents had a 44.9% hard hit rate against him, which led Mariners relievers allowing 100-plus batted balls. The Michigan State product also saw his opponent AVG skyrocket from .219 in July to .351 in September with his in-zone swing and miss rate cratering from 19.6% to just 5% during the same span.

Is the sky falling with Sewald and Misiewicz? No. Seattle’s relievers were pushed hard late in the season. It is possible all that is needed is down time to recover from a heavy workload. Still, Sewald and Misiewicz were vital to the team’s success. Significant regression in 2022 could potentially have a negative impact on the bullpen.

Help Is On The Way

Despite any potential concerns with Sewald, Misiewicz or any other holdover from the 2021 bullpen, it is important to note new names will be added to the high-leverage mix next season. The power arms of Ken Giles and Muñoz, both coming off Tommy John surgery, project to be ready for Spring Training. Assuming good health, both should help depressurize the backend of the 2022 bullpen.

Even if the bullpen unexpectedly falters, President of Baseball Operations Jerry Dipoto and his staff have demonstrated the agility to pivot when the situation dictates. So, there is no need for concern in October.

Besides, the Mariners will once again have Scott Servais getting the most out of his bullpen in 2022.

That is a good thing.

My Oh My…

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Luke Arkins

Luke is a native New Yorker, who grew up as a Mets fan. After the US Navy moved him to the Pacific Northwest in 2009, he decided to make Seattle his home. In 2014, Luke joined the Prospect Insider team. During baseball season, he can often be found observing the local team at T-Mobile Park. You can follow Luke on Twitter @luke_arkins

1 Comment

  1. Lets add back Graveman on a 3 year deal as a player coach and/or generally a bad ass teammate.

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