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Memorial Day has arrived and it’s readily apparent the Seattle Mariners are facing an uphill climb to have any chance of competing for a playoff berth in 2022. What will it take for the Mariners to get back on track before it’s too late?

We’ve already discussed Seattle’s lineup and starting rotation in the first two segments of our Mariners at Memorial Day series. Let’s give some attention to the bullpen. A unit that’s struggled at times over the team’s first 48 games.

Turbulent Times

“Reliever volatility” is a common phrase mentioned during discussions pertaining to a team’s bullpen success from one year to the next. It certainly been on display with the Mariners this season. The strongest unit on last season’s roster has become a liability this year. In 2021, Seattle relievers combined for a .297 xwOBA – sixth best in MLB. This season, the bullpen’s .324 xwOBA ranks 18th.

M's Bullpen Stats and Rankings

So, what’s caused the Mariners’ bullpen to regress from its lofty status? There are several factors at work. Perhaps the most prominent being the majority of the key holdovers from 2021 bullpen have been significantly less effective this season. Several even aren’t on the active roster due to injury and ineffectiveness.

Since we mainly relied on the expected weighted on-base average (xwOBA) of opposing hitters to gauge starter effectiveness in our rotation report, we’ll use the same approach with the bullpen.

As we noted when discussing Seattle’s starters, xwOBA relies on quality of contact (exit velocity and launch angle) to determine what should’ve happened to batted balls without the influence of good or bad defense. Strikeouts and walks also factor into the equation. This means xwOBA captures the most important components of being a successful pitcher – minimizing contact, avoiding base runners, and preventing the most damaging batted balls.

Falling Like Flies

When we compare the 2021 and 2022 xwOBA of key holdovers from last year’s 2021 Mariners bullpen, it becomes glaringly evident where the regression has taken place.

xwOBA of 2021 Bullpen Studs Not As Studly In 2022
Erik Swanson*
Anthony Misiewicz
Paul Sewald
Diego Castillo
Yohan Ramírez**
Drew Steckenrider***
Casey Sadler
* Injured list
** Designated for assignment / traded
*** Assigned to Class-AAA Tacoma
Red = Appreciably Worse Than 2021

Injuries to a pair of key relievers have helped undermine the effectiveness of this year’s bullpen. The first came before Opening Day when Casey Sadler was lost to season-ending shoulder surgery. Sadler was a versatile and extremely effective weapon for manager Scott Servais last season. To date, no newcomer has approached the same level of excellence as the Oklahoman did with the 2021 Mariners.

When Erik Swanson went down with elbow inflammation about three weeks ago, he was already a standout in Seattle’s bullpen serving as a valuable late-inning shutdown reliever. Fortunately for both player and team, the right-handed Swanson is close to returning to action.

In the offseason, I urged readers to not sleep on the potential Yohan Ramirez possessed. Unfortunately, walks continued to plague the 27-year-old as they had throughout his professional career. As a result, Ramirez was designated for assignment by the team earlier this month and subsequently dealt to the Guardians.

Drew Steckenrider was recently optioned to Class-AAA Tacoma when the team could no longer afford to give him more opportunities at the big-league level to correct his issues. That said, getting the former Tennessee Volunteer back on track may be easier than finding someone to replace the late-inning value he provided the Mariners in 2021.

Southpaw Anthony Misiewicz has seen an approximate 2-mph decline in his average four-seam fastball velocity this season, which may or may not mean anything. But there’s no denying Misiewicz isn’t performing at the same level he did in 2020 and 2021.

Simply put, Diego Castillo is an enigma. The right-hander experienced lapses in command shortly after joining the Mariners last July. But his performances this year have ranged from stellar to disastrous. When the native of the Dominican Republic is on, he’s an excellent high-leverage arm. When things aren’t going well, he looks more like a candidate for mop-up duty.

The lone holdover delivering positive results is Paul Sewald, who enjoyed a breakout season with the Mariners in 2021. Sewald remains Servais’ top relief arm. But he’s been more mortal than last year, which is reflected in the jump in xwOBA. His strikeout rate has dropped 14 points from last year to 25.4%, which is still considered above average. The right-hander is also allowing a lot of loud contact. His 46.5% hard-hit and 9.3% barrel rates are well above league norms.

Not only have most of the best arms from last year’s bullpen stumbled to some degree, only a few of the reinforcements brought in to mitigate reliever volatility have delivered positive results on a consistent basis.

xwOBA Of The Replacements
Penn Murfee (.213)
Sergio Romo (.236)
Andrés Muñoz (.315)
RP MLB Average = .324
Matthew Festa (.341)
Roenis Elías (.458)

The most pleasant surprise of the 2022 bullpen has to be Penn Murfee. The 28-year-old rookie hasn’t been thrust into high-leverage situations. But he’s struck out 18 hitters in 15.1 innings and has yet to allow a home run. Perhaps Servais eventually begins giving Murfee an opportunity to make a difference in the late innings of a close game.

Sergio Romo has only appeared in eight games after missing time with shoulder soreness. Therefore, it’s a bit early to evaluate Romo’s numbers. That said, the 39-year-old has ability and pedigree to be a valuable late-inning contributor for the Mariners throughout the season. Only Father Time and health can stand in his way.

Flamethrower Andrés Muñoz has wowed fans with his 100-mph fastball. Unfortunately, opposing hitters haven’t been as impressed. The league has a .545 AVG against his four-seamer. Still, he’s only 23-years-old and his slider has been devasting (.158 AVG). The eyeball test suggests Muñoz has the stuff and the makeup to evolve into a trustworthy late-inning option for Servais.

Two relievers who missed last year due to Tommy John surgery recovery could potentially help the Mariners in 2022, although it’s too early to tell. Three-time Mariner Roenis Elías just joined the team. In recent years, he’s been a versatile, multi-inning arm. Right-hander Matthew Festa has flashed at times, although he recently missed two weeks due to elbow tendonitis and still trying to establish himself in Seattle’s bullpen.

Another preseason health-related setback was Ken Giles, who suffered a finger injury in Spring Training. Giles was recovering from Tommy John surgery when the Mariners signed him signed prior to the 2021 season with the expectation the right-hander would eventually fill a high-leverage role in this year’s bullpen. That has yet to happen.


Even if the healthy holdovers were to revert to their 2021 form, the Mariners will need to find more bullpen help. That’s assuming the club is still serious about contending this year. If the front office determines contention is out of reach in late-July, it’s plausible relievers carrying value will be dealt via the trade market.

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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