A 2025 warning sign that the Mariners have to keep an eye on in 2026

The art of pitching can be a fickle one. Players can be Cy Young contenders one year and optioned the next. Relievers have it the worst, dealing with small sample sizes and for some, the highest-leverage game situations on a regular basis. It's why closers often have short lifespans these days and few ever manage to maintain elite numbers over an extended stretch.

Although their bullpen found immense success in 2025, Seattle still has some reasons to worry about their best relief arm in 2026.

Hidden in Andrés Muñoz's great season numbers are signs of potential regression in 2026

Muñoz has been one of the best relievers around for a few years now, and he hit a new peak last season. He got off to a scorching start, setting a new franchise record for most consecutive scoreless innings for a reliever to start a season. After 64 appearances, he finished with a 1.73 ERA and 2.43 FIP, accumulating 38 saves on the way. All of his peripherals stayed as good as they have been over the past few years, so what is there to worry about?

Pitching analytics has gotten advanced enough for many to suggest that ERA is no longer the best predictor of itself. Instead, more complex statistics like xFIP and SIERA tend to be relied on more for projecting what a pitcher will accomplish in the future. Muñoz had a season xFIP of 3.05, which is still pretty solid but some months were far better than others.

From June through August, he had an xFIP of 3.68 over 28.2 innings, a mark far closer to league-average for relievers. His FIP was still solid over that span but that can be explained by the difference in how the real stat and expected stat are calculated. In essence, xFIP uses the league-average percentage of fly balls that ended up as home runs instead of actual home runs allowed in its formula. The idea is that pitchers have the most control over how many fly balls they give up versus how many end up leaving the park which could be affected by a litany of reasons.

His season xFIP of 3.05 placed him 20th among qualified relievers and his peer group included Bryan Abreu, Aaron Ashby, and Phil Maton. However, the 3.68 xFIP he maintained during the summer would've placed him on par with more middle-of-the-road bullpen arms like Matt Festa, Ryan Walker, and Taylor Clarke.

Muñoz also lost a considerable amount of velocity on his fastball over the course of the season, averaging 99.3 MPH in June before gradually decreasing to 97.7 mph in August. It's a trend that has been prevalent throughout his career but unlike in previous years, the velocity didn't come back towards the end of the season, potentially due to his increased workload.

Statistical dips over small sample sizes should never be taken as gospel, and he'll still serve as the team's closer for 2026, but they can't simply be swept under the rug either. He's hardly in the hot seat like some of his teammates, but if the warning signs lead to real regression, Seattle may have already gotten his understudy this winter.