Mariners bullpen is a glaring example of how ERA lies about relief pitchers

With the way things have been going, it may be surprising to hear that the Mariners have one of the best bullpens around, at least according to some numbers. Seattle's relievers have combined to post a 3.44 ERA (8th in MLB) and a 3.51 FIP (4th in MLB).

This places them in elite territory but to many fans, it doesn't pass the eye test. The front office has already gotten to work making cuts and taking bets on untested arms. But if the numbers have looked solid so far, why the bearish outlook?

Seattle's reliever ERA obscures the team's pitching struggles in crucial situations

ERA and FIP are great but like every statistic in baseball, they're not perfect. Especially this early in the season, these numbers are subject to big swings. Andrés Muñoz hasn't looked his best this year, but he's certainly better than his 8.00 ERA would lead you to believe. On the other hand, Cooper Criswell likely won't be able to maintain his 1.64 ERA for very long. This is especially relevant for relievers who pitch small samples and often get three outs at a time.

More importantly, ERA and FIP are calculated independent of leverage. Posting a 2.50 ERA as a middle reliever isn't nearly as impressive as posting a 2.50 ERA as the team's closer. But if ERA and FIP aren't great indicators of quality thus far, what numbers should be looked at to explain why it has been a nail-biting experience to watch the Mariners bullpen in 2026?

WHIP is a good start since it represents total traffic allowed. If a reliever loads the bases with three singles and then escapes the jam, their ERA won't reflect negatively but it's a tense situation nonetheless. Seattle relievers have a WHIP of 1.38 (16th in MLB) and two of the worst offenders on the team, Jose A. Ferrer (1.73) and Andrés Muñoz (1.56), have also been the toughest to watch at times.

While it gives a clearer glimpse of total traffic, WHIP still doesn't weigh higher-leverage situations more heavily. Instead, looking at Win Probability Added suggests that the Mariners' bullpen has a WPA of -1.16 (25th in MLB). So despite the team's relievers posting solid numbers overall, they've fallen short in the most critical moments.

An example of a particularly impactful collapse of the bullpen was Seattle's game against the Athletics on April 20th. The Mariners headed into the 8th inning tied at 3-3 before Casey Legumina allowed three earned runs. Seattle's lineup scored just one run in the ninth which would've been enough to secure the win if they'd managed to keep the Athletics scoreless.

Being a relief pitcher in the big leagues is notoriously difficult. It's a mercurial position that stands in sharp contrast to the consistency of starting pitchers which is why they must also be evaluated differently. The statistical discrepancy of Mariners' bullpen means that they've had their moments but when the lights have been the brightest, they've failed to step up.

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