No player has helped their team win this year more than Andrés Muñoz.
By the traditional metrics, Muñoz should easily take home AL Reliever of the Month for April. He finished the month with 19 strikeouts, 11 saves and zero runs allowed. But Muñoz wasn’t just highly effective in April — he was highly effective in crucial moments.
Muñoz leads MLB in Win Probability Added (WPA) at 2.16. While most advanced metrics are context neutral (a homer is a homer is a homer), WPA measures how much any event in a game contributes to a team’s chance of winning — i.e., a grand slam down three in the bottom of the ninth is worth more than a solo shot in the middle innings of a blowout. WPA can be seen in the movement of the line in the “win expectancy” charts we share after games. No player in MLB has moved their team’s line towards victory more than Muñoz. (Technically, Jorge Polanco leads MLB in WPA at 2.19, but he hasn’t played enough to qualify. Both are far ahead of the runners up.)
It’s the most impactful stretch of Muñoz’s career.
This is mostly because Muñoz has been, in a word, dominant. And, in two words, dominant often. His 1.75 FIP would be the best mark of his career. His whiff rate and strikeout rate are as good as ever. He’s walked just two batters over the last four weeks. While he’s given up a bit of hard contact, most of it has been on the ground. His 72.4% ground ball rate is top five in MLB. These grounders have not only helped him get out of games but (perhaps) into games, too.
“Contact often times saves you pitches,” Dan Wilson recently told Lookout Landing. “It allows you to come back the next day … allows you to get more opportunities.”
Muñoz isn’t exactly pitching to contact now — his profile is still largely based around whiffs and strikeouts. But the grounders-turned-to-out have helped push his BABIP down to .179, top 10 in MLB. He’s been an outs machine, and he’s had a few ultra-quick outings because of it.
Muñoz the closer
This brings us to the more controversial reason for Muñoz’s outsized April impact. Muñoz is now the Mariners true closer, which is a new role for him, and a strategy we haven’t seen the team employ in years.
Now, I’m going to do some editorializing here first: I don’t like this, and I will never like this. Closers are, in my personal opinion, bad strategy. Saving your best reliever for a very specific situation — the ninth inning with a lead — is simply not how most teams have operated in the “enlightened” age of baseball. A team should do what it can in the moment to preserve a lead in jeopardy, rather than waiting for an equally crucial spot that may never present itself.
We’ve seen this “closer” strategy backfire already. In Cincinnati, the Mariners held a two-run lead in the eighth inning. Wilson turned to Eduard Bazardo, who got an out before loading the bases. The next batter was the highest leverage moment of the game and one of the biggest spots Mariners pitchers have faced all season. In the past, this is where Scott Servais would have turned to Muñoz to try to wiggle out of the inning, even if it meant a five-out save. It almost always worked. Instead, Wilson stuck with Bazardo, who gave up a grand slam and the lead. The Mariners would battle back and eventually win, but by the time Muñoz stepped to the mound, the Mariners were up four, and it was the lowest leverage spot of the game. It’s the perfect example of why “saving” your closer for a specific scenario doesn’t always work, because that scenario doesn’t always exist.
But it’s also an example of why the modern manager is valued more for their ability to speak to the press than their explicit tactical insight. The gap between a good and bad managerial decision is often closed by “baseball will baseball.” There are infinite counterfactuals in bullpen usage, and the true “value” difference between Muñoz the closer and Muñoz the fireman is negligible over 162 games.
And, ultimately, it’s kind of hard to argue with Muñoz’s usage so far. Not only does he lead Mariners relievers in average leverage when entering the game, he’s second in all of baseball. Only Kyle Finnegan of the Nationals has pitched in bigger spots (and not nearly as many of them). Muñoz’s average leverage this year is roughly equivalent to what it was last year when he was used as soon as necessary. That’s because, all else equal, the ninth inning is the highest leverage inning of the game. If you can get to there with a lead, it’s the place where you want your best reliever. The rest of the Mariners bullpen hasn’t always helped in that regard, but the lineup has.
And because he’s not asked to pitch as much within a game, he’s been able to impact more total games. With 15 appearances, Muñoz has influenced exactly half the Mariners games this season and nearly all their wins. He didn’t get into his 15th game until May 12 last year, and he’d thrown 30 more pitches in the process.
Muñoz the closer is working for now, even if I don’t fully agree with it. He’s pitching effectively and in big spots and often. If April is any indicator, we’ll see Muñoz cap plenty more wins this summer.
