Last Updated on March 20, 2018 by Luke Arkins

As the Seattle Mariners prepare for the regular season, the club’s bullpen is viewed as a strength. Having said that, what exactly should Seattle fans expect from their favorite club’s relievers his year?

In the third week of March, it’s tough forecasting with any certainty how anything will go for a team. At this point last year, the Mariners’ projected rotation was Felix Hernandez, James Paxton, Hisashi Iwakuma, Drew Smyly, and Yovani Gallardo. By May, only Gallardo remained uninjured.

Putting aside the potential for injuries — yes, that’s hard to do with so many Mariners banged up this month — let’s presume the relievers remain relatively healthy. How should we establish expectations for the bullpen?

To address this question, I’m turning to a metric Mike Petriello of used in a piece a few weeks ago — expected weighted on-base average (xwOBA).

When discussing the Oakland Athletics’ roster, Petriello referred to xwOBA as he evaluated the club’s new relievers. This motivated me to take the same approach with the Mariners’ bullpen.

If you haven’t heard of xwOBA before, it’s a relatively new Statcast product found at Baseball Savant. It uses quality of contact (exit velocity and launch angle) and outcomes not requiring defense (strikeouts and walks) to determine what should’ve happened to balls put in play.

Pitchers and hitters can affect exit velocity, launch angle, strikeouts, and walks. However, they have virtually no control over a ball once it enters the field. By reviewing the xwOBA of opposing hitters against Mariner relievers, we can gauge their 2017 effectiveness sans defense or luck.

Yes, using xwOBA isn’t an ironclad method for projecting future performance. But what approach is? Just consider this exercise an opportunity to look at Seattle’s bullpen through a different lens.

Before discussing individuals, let’s see how the cadre of relievers Mariners general manager Jerry Dipoto has collected compares to the current bullpens of other clubs.

The following chart illustrates the number of relievers on each AL team, who faced at least 100 hitters and were in the top 50-percent of the major leagues for xwOBA last year (.295 or lower).

It’s worth noting starter Erasmo Ramirez was among the top 50-percent for relievers last season, but I excluded him. Even without Ramirez, Seattle fares well when compared to their AL competition.

Am I suggesting on March 20 that Mariners relievers will be on par with the Baltimore Orioles or better than the Cleveland Indians. No, but Seattle’s standing — based on last year’s data — fuels optimism their bullpen could deliver in a good way this year.

Okay, let’s turn our attention to individuals. The following table includes the ten current Mariner relievers who faced at least 100 batters last year. Next to each player’s name is their MLB rank among the 254 pitchers meeting the 100 batters faced criteria.

2017 MLB Rank
Edwin Diaz
Juan Nicasio
James Pazos
Nick Vincent
Chasen Bradford
Marc Rzepczynski
Erik Goeddel
David Phelps
Casey Lawrence
Dan Altavilla

Many of you won’t be surprised to see closer Edwin Diaz atop the Mariners’ list, although former teammate Emilio Pagan (.241) actually led the club. Still, seeing Diaz in the top 15-percent of major league relievers is encouraging.

In 2016, Diaz posted relatively the same xwOBA (.252), so there’s no reason to believe he can’t stay at his current level of excellence. But the issue going forward is whether the right-hander can bloom into something special. Becoming more consistent would help.

Last year, Diaz’s 11.5-percent walk rate ranked in the bottom 15-percent among 150 relievers with 50-plus innings. Yet, he induced the fifteenth most swinging strikes and had the eighth lowest line drive rate.

Considering he’s still just 23-years-old, it’s easy envisioning Diaz becoming one of the best relievers in baseball. Perhaps 2018 will be the year he takes the next step.

Last season was the first Juan Nicasio served as a full-time reliever. Nicasio didn’t miss bats as often as Diaz did, but he displayed better control and a knack for avoiding damaging hard contact.

Nicasio’s 6.9-percent walk and 7.8-percent home run/fly ball rates were in the top 25-percent among relievers last season. If he can repeat that success, the hard-throwing righty will be a valuable late-inning piece for manager Scott Servais.

James Pazos placed in the top-30 percent with his .282 xwOBA and still has room to improve. The lefty had the tenth lowest hard contact rate in baseball last season. Moreover, he maintained a 27.1-percent strikeout rate.

That said; Pazos did struggle with right-handed bats. The native Arizonan had the fifth highest average exit velocity against righties among lefty relievers. Furthermore, he was particularly susceptible to surrendering walks and home runs to opposite-handed bats.

The keys to success for Nick Vincent last year were pinpoint control and avoiding the long ball. Vincent had the eighth lowest walk rate (5-percent) among 150 relievers, while his 3.3-percent home run/fly ball ratio was second best. That’s exceptional considering his fly ball rate was fourteenth highest.

Still, Vincent’s 2017 home run/fly ball rate was nearly 11 points lower than the season prior. Whether the 31-year-old can repeat that success in 2018 merits observation.

To be honest, I was surprised Chasen Bradford placed so high on the xwOBA list. Then again, his 55.9-percent ground ball rate was thirtieth best among 235 relievers with 30-plus innings.

It’s unknown whether Bradford makes the club out of Spring Training, but the 28-year-old could prove to be an under-the-radar pick-up who delivers positive results this year.

Over the last two seasons, lefty Marc Rzepczynski has been relatively effective against left-handed hitters. But he’s walked 23.7-percent of righties faced since 2016. Adding to the 32-year-old’s woes, his average exit velocity against righty bats was eighth worst among southpaw relievers.

Barring unforeseen circumstances, brand new addition Erik Goeddel won’t make the Mariners’ Opening Day roster.

In 29 innings with the New York Mets last season, Goeddel was adept at missing bats (24.7-percent strikeout rate), but had a 25-percent home run/fly ball rate.

Having said that, injuries have been an issue for the 29-year-old. As Prospect Insider founder Jason A. Churchill noted, Goeddel could prove value, if he can stay healthy.

The most intriguing reliever in Seattle’s bullpen is David Phelps — at least he is to me.

Acquired last July by Dipoto, Phelps had a below average .316 xwOBA during his combined time with the Mariners and Miami Marlins. That’s significantly higher than the season prior (.265).

Phelps’ average exit velocity and walk rate remained relatively stable between 2016 and 2017. But he saw a six-percent decline in strikeouts with a similar increase in hard contact.

Perhaps the issue requiring an elbow procedure last September factored into Phelps’ regression last year. Assuming the 31-year-old is healthy, it’s reasonable to expect a bounce back to his 2016 numbers.

Dan Altavilla is another interesting case. He had the fifteenth highest fly ball rate, just one spot behind Vincent. But the 25-year-old gave up significantly more hard contact and home runs. Moreover, he walked batters twice as often as Vincent.

Still, there are reasons to be upbeat about the 2018 version of Altavilla. Seattle Times beat writer Ryan Divish noted last month the right-hander made offseason adjustments to his delivery designed to improve command. He also adopted the slider grip used by teammate James Paxton.

So what are my expectations for Mariner relievers this coming season?

It’s reasonable to view Seattle’s bullpen as a cornerstone to the club’s 2018 success. The heights they ultimately reach depends on the development of the young trio of Diaz, Pazos, and Altavilla and the effectiveness of Phelps.

At least that’s how I see it on March 20.

Follow Luke!
Latest posts by Luke Arkins (see all)


  1. Avatar

    With Phelps out for the year and in need of TJ surgery, since he is a free agent after the season, can the Mariners release him before the start of the season and only pay him a small portion of the salary?

    Perhaps the money saved can be used to acquire another reliever.

    I didn’t like the Emilio Pagan trade this offseason. I hope it doesn’t come back to haunt us. Pagan’s spring training numbers have been mixed (7 ip, 3 HRs).

  2. Avatar

    Have to put the Phelps injury on Churchill. The rant on how the Mariners are not snakebit was a clear challenge to the baseball gods.

    Will need some kind of small animal to sacrifice lest the whole staff goes down.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.