The last thing the Mariners need is a problem with Andrés Muñoz

Let's be clear that Andrés Muñoz is one of the best relievers in baseball. Of all the bullpen arms in MLB, he has the fourth-highest Win Probability Added (3.3) and has the third-most saves (31). Cap it all of with a 1.72 ERA over 52.1 innings, and it doesn't seem like there's anything to worry about.

However, a closer look at his numbers show that he might be heading in the wrong direction.

Andrés Muñoz has had a shaky August and hasn't looked nearly as dominant

In the first half, he was nearly untouchable. He had a 1.50 ERA, a WHIP of 0.89, and a strikeout rate of 32.4. In fact, it took until May 30th before he gave us his first earned run. Prior to August, he was sitting pretty at a 1.32 ERA and a 0.93 WHIP.

However, he has posted a 3.18 ERA and 1.59 WHIP this month, a steep decline compared to where he was at before. He has had some issues dealing with heat and dehydration in some of his recent outings, but even in the more temperate Seattle environment, he has allowed more traffic than usual.

He has punched out just 23.1 percent of opposing hitters this month and is missing far fewer bats, managing a swinging strike rate of just 13.0. A major contributing factor to this is regression on his four-seam fastball. For the first time since 2022, his four-seam fastball has been worth negative run value and hitters have been averaging .318 and slugging .523 against his heater.

To his credit, some of the pitches that do go for hits are good pitches, such as this outside fastball that Jake Cronenworth nearly hit out on Wednesday:

But others are left far too close to the middle of the strike zone, like this middle-middle heater that Michael A. Taylor crushed for a homer on August 6:

Muñoz's pitch usage hasn't actually changed much, but this may push him to be more dependent on his slider, especially since his sinker has also seen poorer results as of late. While his slider is one of the best in the business, a lack of diversity in his arsenal could give hitters a big advantage, especially as we approach the postseason.

The Mariners' closer is hardly the only concern on the roster and as a team, they have plenty of problems to fix before they're ready to make a deep run in October. But after a season of lockdown saves and lights out pitching, it feels strange to see Andrés Muñoz transition from bullpen bedrock to rocky reliever.

The chaotic nature of baseball means these performance valleys come with the territory, so there's still a chance he's able to re-adjust and regain the life on his fastball in the final month of the regular season. Now that the AL West is all but out reach for Seattle, they'll need every advantage they can get to retain their Wild Card spot.