Analysis: Moving Forward, Mariners Will Have Top-5 Bullpen in Baseball
The Mariners recently designated two of their bullpen arms, Sergio Romo and Roenis Elías, for assignment. Neither had been particularly helpful for a struggling bullpen that currently ranks 16th in baseball with an ERA of 4.04.
Although Elías has gotten decent results, his peripheral and predictive stats were concerning, while seemingly in a low-leverage role moving forward. The fact that Seattle chose to DFA Elias over someone like Ryan Borucki (and his 8.18 ERA) indicates it is confident in Borucki figuring things out, which could be exciting for some and terrifying for others.
Looking at the glass half full, however, and with the returns of Ken Giles and Erik Swanson, I am going out on a limb and declaring that the Mariners will have a top-five bullpen the rest of the season.
There are plenty of reasons to be optimistic. The Mariners' bullpen has a cumulative K-BB percentage of 18 percent, which is good for the third-best in the majors. They also have the eighth-best called strike plus whiff rate at 28.8 percent. They are good at avoiding walks and striking people out—that's the name of the game, no?
By removing Romo and Elías, Seattle is essentially replacing two of its pitchers with the lowest K-BB rate (Romo is at 10 percent this season and Elías is just below nine percent; the MLB average is 14.1 percent) with Swanson and Giles.
As a whole, the bullpen has the third-worst home run to fly ball rate in baseball and, given the pitcher-friendly reputation of T-Mobile Park paired with the peripherals of individual relief pitchers who are struggling with giving up home runs, I do not expect that to continue.
The Mariners' bullpen has also logged the fourth-fewest innings this year, which means that, while it has been a weakness, it has not been overexposed. This also means that some of the following pitchers may not have large enough sample sizes to predict their future performances this season—specifically Tommy Milone and Giles (the latter I did not insert into this table after just one inning).
| Ryan Borucki | Diego Castillo | Tommy Milone | Andrés Muñoz | Penn Murfee | Paul Sewald | Erik Swanson | MLB AVERAGE (RP) | |
|---|---|---|---|---|---|---|---|---|
K-BB% | 9.3% | 20% | 9.5% | 30.1% | 23.3% | 18.2% | 38.5% | 14.1% |
HR/FB | 30% | 9.1% | 10% | 26.3% | 0% | 13.3% | 11.1% | 10.7% |
CSW% | 28.4% | 29.1% | 27.7% | 33.2% | 30% | 31.5.% | 31.2% | 28% |
Pitching+ | 100.7 | 97.5 | 107.2 | 110.7 | 110.9 | 114 | 112.9 | 100 |
Entering June 22, there are plenty of reasons for Mariners fans to be optimistic about the future performance of the bullpen. Giles will likely provide some value to the club, and there is also the potential for outside additions to be made.
That said, I strongly believe this group will be a top-five bullpen in the MLB going forward, with the only weak link seeming to be the lefty specialist Borucki, who I still think can find success with the right adjustments.
