2023 Mariners Season Postmortem

Missing the playoffs was sticking in my craw – and what am I gonna do, watch the Astros in the ALDS? – so I thought I'd write up a little postmortem. You probably know all of this stuff already, but just in case, thought I'd lay it all out in one place. In a couple weeks I might write up an offseason plan that refers back to this, we'll see.

2023 Postmortem

The Mariners had an unsuccessful 2023 season, failing to reach the playoffs. Continued excellence from their pitching staff, Julio Rodríguez, and Cal Raleigh, plus a career year from J.P. Crawford, were offset by failed offseason acquisitions, struggles with situational hitting, and the unexpected breakout of the Texas Rangers, leaving the 88-win Mariners on the outside looking in.













MLB rank












In this postmortem of the 2023 season I’ll examine what went wrong, what went right, and what we can learn from this year’s Seattle Mariners.

What went wrong?

Failed offseason additions

No way around this one. The Mariners’ three primary offseason acquisitions were Teoscar Hernández, Kolten Wong, and A.J. Pollock. To get these guys, they traded Erik Swanson, Adam Macko, Jesse Winker, and Abraham Toro; they also paid the trio a combined $31M.

  • 2022 Hernández, Wong, and Pollock: 5.3 WAR, 2.6 WPA

  • 2023 Hernández, Wong, and Pollock: 0.1 WAR, -2.5 WPA

Wong and Pollock in particular were unplayably bad and both were essentially cut before the trade deadline. The Mariners also gave significant playing time to offseason acquisitions Cooper Hummel and Tommy La Stella, both of whom produced negative WAR.

Frustratingly, despite an injury-ridden year for Mitch Haniger in San Francisco, the Mariners’ departing free agents (Haniger, Adam Frazier, and Carlos Santana) produced about 2 more WAR and 3 more WPA than Hernández, Wong, and Pollock for only $29M ($2M less). The Mariners lost the AL West by 2 games; if they’d simply run the 2022 lineup back out there they might’ve won it instead.

The pitching ran out of gas

Even with their lineup struggles, the Mariners entered the month of September in first place in the AL West. Their division rivals helped them out in September, too, with both teams playing .500 ball and Houston in particular going 2-7 against Oakland and Kansas City. If the Mariners had stayed at .500 for the month, they would’ve won the division.

Unfortunately, their pitching, which had been rock solid all year, did this:

SEA pitchers in…





3.64 (1st in MLB)

3.69 (1st)

19.2 (2nd)


4.19 (13th)

4.77 (21st)

1.0 (24th)

With only two off days the entire month, and with their rookie pitchers throwing by far the most innings of their careers to date, the Mariners’ pitching staff ran out of steam. Bryce Miller posted a 6.08 ERA in September, and Luis Castillo was shelled in both of his critical starts in the Mariners’ final 10-game homestand. In the bullpen, only Matt Brash maintained his standard of excellence, while Saucedo, Speier, Topa, Thornton and Muñoz all posted negative fWAR.

The Mariners really could’ve used Robbie Ray and Marco Gonzales this year to prevent Miller and Woo from having to throw so many innings. Overtaxed rookies leaving short starts early in September forced the bullpen to cover more innings in September than it did in any other month all season, just as it was struggling most. As the saying goes: you can never have too much pitching.

Poor performance in close games

The Mariners’ W-L record underperformed their underlying statistics. By Pythagorean record, they "should" have gone 92-70 and been the third Wild Card, while by BaseRuns they actually "should" have been WC1 (ahead of Baltimore, Houston, and Toronto). Unlike in 2021 and 2022, however, the Mariners underperformed in one-run and extra-inning games. Going 6-14 in extra innings was particularly painful.

A lot of the attention here has fallen on Julio, who was stellar in late-and-close situations on the road but struggled in the clutch at home. Actually, though, the biggest offender was Teoscar Hernández, who posted a 54 wRC+ in high-leverage situations overall (vs. Julio’s high-leverage wRC+ of 122) and had a -1.31 WPA. Cal Raleigh and Ty France also struggled late-and-close, with wRC+es under 80 in high-leverage spots, while Matt Brash was cursed by the BABIP gods in important spots early in the season.

There’s maybe some credence to the idea that high-contact offenses perform better in extra innings due to the zombie runner rule. The Mariners were second in MLB in strikeouts, behind only the Twins – but those same Twins went 12-8 in extras. If the Mariners think it would help to focus their practice on executing in late-and-close situations, they could try it, but probably this is all random. Over a large sample size there’s no such thing as clutch in MLB.

The Texas lineup went supernova

Despite going 9-4 against the Houston Astros, who looked uncharacteristically vulnerable en route to their worst 162-game record since 2016, the Mariners didn’t even come in second in the AL West. They were passed by the Texas Rangers, who weren’t projected or predicted to compete for the division. Seattle went 4-9 against Texas, including a backbreaking September three-game sweep in Arlington.

Much has been made of the Rangers’ aggressive spending and pitching acquisitions, but interestingly, their 2022 offseason wasn’t actually very successful. Between the offseason and trade deadline, Texas committed $264M and traded two 50 FV prospects to acquire Jacob Degrom, Max Scherzer, Nathan Eovaldi, Jordan Montgomery, Andrew Heaney, and Martín Pérez. Those 6 starters combined for 8.7 fWAR in 575.2 IP, quite a bit worse than Texas was hoping for; Degrom and Scherzer are currently injured, while Montgomery and Pérez will be free agents at season’s end.

The real secret to Texas’ success was their offense, which led the American League in fWAR and runs scored after being only 10th-best in the AL in 2022. Especially surprising was that they did this with essentially the exact same personnel, adding only Robbie Grossman in the winter. In a nutshell, a whole bunch of Rangers had the best year of their career, all at the same time. Marcus Semien and Corey Seager were 2nd and 3rd in the AL in WAR. Those two plus Adolis García, Josh Jung, Jonah Heim, Leody Taveras, and Mitch Garver combined for 16 WAR in 2022… but 29 WAR in 2023, a massive leap forward for Texas’ offense.

The good news is this is unlikely to repeat in 2024. Fangraphs projects those named Rangers hitters for 8 WAR of regression, and Corey Seager and Marcus Semien won’t be the two best non-Ohtani hitters in the AL forever. But the Mariners’ lack of investment in the 2022 offseason left them vulnerable to a breakout like this, and now they’ll have to contend with the Rangers’ continued spending and the debuts of new prospects like Evan Carter and Wyatt Langford.


The Mariners’ offseason hitting acquisitions collectively sucked, their pitching collapsed in September, they were bad and/or unlucky in extra-innings games, and the Rangers’ hitters all had career years at the same time. If any one of those things had broken differently, the Mariners would probably be hosting the ALDS right now. Bummer.

What went right?

As in any postmortem, while it’s tempting to focus exclusively on what went wrong, it’s also worth calling out what went right and celebrating wins that the team can learn from or try to repeat. I’ll be more succinct here, but all of these positives are why the Mariners got so close to the playoffs to begin with.

The Mariners have the best center fielder in baseball

Reports of a "sophomore slump" were greatly exaggerated. Julio has the most WAR of any CF since he debuted, and he’ll be a Mariner for the next decade.


…and a bunch of other awesome young major leaguers too

Who’s the best catcher in the AL since 2022? That’s easy, Adley Rutschman (10.5 fWAR). But did you know that Cal Raleigh, with 8.8 WAR, is #2? And that he’s closer to Rutschman than #3 (Jonah Heim, 6.8) is to Cal? Big Dumper somehow wasn’t on Fangraphs’ top 50 trade value list, but the author later admitted he probably should’ve been.

Speaking of the trade value list, Logan Gilbert and George Kirby were #33 and #26. And don’t forget about Andrés Muñoz and Matt Brash! The Mariners have an awesome, young, controllable core of players just entering their primes. They should put them in the playoffs, or something, I dunno.

J.P. Crawford went to Driveline and doubled his career high in HR

J.P.’s winter work at Driveline Baseball helped add 2 MPH to his bat speed, leading to him more than doubling his career best in home runs. He says he plans to go back and take Ty France with him, which would be great, since Ty’s lack of power production at 1B has been a real problem since his 2022 wrist injury.

(Incidentally, I’ve seen fans giving France and Eugenio Suárez a lot of grief for their hitting in 2023. This is not really fair to Geno; note that the Mariners were 7th in WAR from 3B and 19th in WAR from 1B – gah! Positive! This is the section where I’m keeping it positive!)

The bullpen devil magic continues

In 2021, the Mariners had baseball’s eighth best bullpen ERA. Then they lost Drew Steckenrider, Casey Sadler, Kendall Graveman, JT Chargois, and Joe Smith. So in 2022, having turned over basically their whole bullpen, the Mariners proceeded to… have baseball’s sixth best bullpen ERA.

In 2023, with key 2022 relievers Erik Swanson traded, Penn Murfee hurt, Diego Castillo demoted, and Paul Sewald eventually-also-traded, the Mariners… had baseball’s fourth best bullpen ERA. This year’s success stories were Gabe Speier, Justin Topa, and Trevor Gott, who they plucked off of other teams’ scrap heaps and got 2.2 WAR out of. Man, whatever the pitching dev gurus are doing over there, it’s working.

The Paul Sewald trade was good actually

Speaking of relievers. Let’s play "spot the outlier".

Josh Rojas in…



Arizona, 2021


1.8 (550 PA)

Arizona, 2022


2.7 (510 PA)

Arizona, 2023


-0.3 (216 PA)

Seattle, 2023


1.2 (134 PA)

I love Paul Sewald. I miss Paul Sewald. Josh Rojas was worth more WAR in Seattle after the trade than Paul Sewald was worth in the entire 2023 season. The Diamondbacks have Sewald for one more year, while the Mariners have Rojas for three more years, and also they have Dominic Canzone and Ryan Bliss too. Cal Raleigh was right about signing free agents, but he was wrong about this trade, which was good, actually.

…José Caballero? wat?

The winner-in-a-landslide of 2023’s "best Mariner that I truly had no idea was in the organization" award is José Caballero. Cabby came out of nowhere when Dylan Moore was hurt and Kolten Wong sucked to post an implausible 2.2 fWAR (!) in only 280 PA. That’s more than Whit Merrifield. The Mariners got this guy in 2019 for literally Mike Leake. He was just, like, chillin’ in AA.

Can he do it again next year? Probably not. Would I find his pitch clock antics amusing if he were on any other team? Definitely not. Did he basically save the 2023 season? Hell yeah.

Last but not least: Miller and Woo

I wanna close with a shoutout to Bryce Miller and Bryan Woo, who stepped up when Robbie Ray and Marco Gonzales went down and were everything the Mariners could’ve hoped for. Thanks to them and Caballero, the Mariners were third in WAR from rookies this season. Miller and Woo blew past their previous innings highs and, despite not yet having polished secondary stuff, were above average major league pitchers for 219 combined innings. It’s maybe easy for modern Mariners fans to forget, but for most teams, not every pitching prospect who makes the bigs is an immediate success story. Miller and Woo did awesome.

It’s too bad that at least one of them probably isn’t a Mariner next year. But I’ll get to the offseason plan, and trade proposals… next time. Thanks for reading!