The Unsung Heroes of the Mariners’ September Surge

The Mariners are entering the final weekend of the regular season with their best shot since 2016 at breaking their infamous postseason drought, having gone 18–8 in September and won 11 of their last 13 games after losing a crucial series to the Red Sox mid-month. Earlier this morning, Jay Jaffe took a look at the bigger picture for the Mariners, their negative run differential, and the historic positive turn of their playoff odds. But this climb up the standings wouldn’t have been possible if it weren’t for some unheralded performances by a number of players on their roster.

From a season-long perspective, the Mariners’ offense has been lackluster, with a wRC+ of 94, ranking tenth in the American League. That went up to 103 in September, but the driving force behind the improved offense has been excellent performance in tight situations. Seattle has the most clutch offense in recorded MLB history (WPA records only go back to 1974), which goes a long way toward explaining the team’s 33–18 record in one-run games this year.

Clutch hitting can take a team far, but it’s not something that can be counted on every night. Luckily, the core of the Mariners’ lineup started hitting extremely well during the final month:

After shuffling through a number of early-season contributors, the lineup stabilized after the All-Star break — something that coincided with Kelenic’s second call-up from Triple-A after his rough debut in May. The hits didn’t start falling immediately after his return to the majors; from July 16 through the end of August, he posted a .181/.263/.315 line (a 65 wRC+) with a 30.5% strikeout rate. But something clicked once the calendar turned over to September, with Kelenic hitting .242/.321/.537, good for a 135 wRC+. His strikeout rate dropped to 25.5%, he launched seven home runs, and more than half of his hits went for extra bases.

Along with his hot streak, the rookie has shown a penchant for collecting timely hits. None were bigger than the go-ahead, two-run double he hit on Wednesday night off Frankie Montas.

A month ago, it would have been difficult to imagine Kelenic catching up to a 95-mph fastball located up and away. He’s actually performed well against major league fastballs — it’s offspeed and breaking stuff that’s really given him fits — but the location Montas hit with his heater was a perfectly executed pitch to take advantage of a significant hole in Kelenic’s plate coverage.

That double was worth .314 WPA — par the course for Kelenic, who accumulated 0.95 WPA in September with a 0.64 Clutch score that was the 10th-highest mark in the majors that month. That has to take some of the sting out of the early-season lows.

The man who drove the Mariners’ offense in September has overcome his own tragic lows. After missing most of the 2019 season and all of last year due to a freak groin injury, Haniger has had a comeback season for the ages.

After missing all of last season, Mitch Haniger of the @Mariners now has 37 home runs this year.

That's the 3rd-most HR in MLB history by a player who didn't play a game in any professional league the previous year, behind Willie Mays (41 in 1954) and Ted Williams (38 in 1946).

— Stats By STATS (@StatsBySTATS) September 28, 2021

In this comeback campaign, Haniger has launched 38 home runs, blowing by his previous career high set in 2018. That power outburst is largely driven by the highest barrel and hard-hit rates of his career. It’s also a step forward from his pre-2019 approach, when he was selling out for home runs with a pull rate over 50% and an average launch angle of 17.8 degrees. That resulted in a .244 ISO, but all that power was marred by a 28.6% strikeout rate and 10.2% pop-up rate. This season, his batted ball profile is more in line with his breakout 2018 season, and his strikeout rate has dropped by more than four points.

Setting the table for Haniger and the middle of the lineup is Crawford. After winning a Gold Glove last year, he’s paired his excellent defense with a league-average offensive line. In September, though, he came through with a .315/.374/.477 line, nine multi-hit games, and 12 extra-base hits. His offensive improvements this season stem from improved conditioning and weight training in the offseason, as well as a better understanding of his ideal approach at the plate. In the past, Crawford was over-focused on power, believing that he had to hit 20 home runs per year to contribute offensively, which caused his swing to get long. This year, he’s been much more direct to the ball, taking it where it’s pitched and using the entire field. The result: His pull and fly-ball rates are both at career lows, and his contact rate is a career-high 86.6%.

As for France, Seager and Torrens, they all came up with big hits in big situations in September. A wrist injury derailed France in May, but since returning from the Injured List, he’s hit .312/.379/.471 (139 wRC+) and played good defense at first base. Seager, who is playing out what will likely be his final year in a Mariners uniform, didn’t contribute as much last month as the names above, but he ranked sixth in our Clutch stat in September. Like Kelenic, Torrens was sent down to Triple-A midseason, but upon his return to the majors on June 15, he blasted five home runs in an eight-game span and has settled in as the Mariners’ semi-regular designated hitter, hitting .267/.331/.477 (123 wRC+) since that second call-up.

The hitters aren’t doing it alone, though. The Mariners’ bullpen was also crucial to this late postseason charge. Paul Sewald has deservedly gotten most of the headlines among the relievers, though he stumbled a bit in September. But the real reason why the relief corps has been so successful is because it hasn’t had to rely on one key pitcher.

These four pitchers have formed a four-armed Machamp that has held the line in any high-leverage situations this September. Castillo was the big trade deadline acquisition after the Mariners dealt away previous relief ace Kendall Graveman. His time in Seattle hasn’t been immaculate: He allowed five runs in 9.1 innings before hitting the IL with shoulder inflammation in mid-August and another four runs in 12 innings since being activated at the start of the month. Nonetheless, he seems to have earned the trust of manager Scott Servais; a 32.7% strikeout rate and minuscule 4.1% walk rate last month likely helped him keep his spot high on the pecking order.

With Sewald and Castillo getting deployed in the highest-leverage situations no matter the inning — usually in the seventh or eighth — the Mariners turned to Steckenrider to close out most of their games in September. He collected six saves last month, and outside of a three-run disaster against the Red Sox on September 14, he allowed just a single run otherwise.

But the member of the bullpen that has gone mostly unnoticed despite a long stretch of phenomenal performances has been Sadler, who is currently in the middle of a 25-inning, 24-appearance scoreless streak that stretches back to July 27. He doesn’t have the gaudy strikeout rates of Sewald or Castillo, but he’s been just as effective by inducing tons of weak contact and allowing just a single home run this season, with a 61.7% ground-ball rate that is the ninth highest in the majors (minimum 30 innings).

Perhaps most impressive about the Mariners’ bullpen is that Sewald, Steckenrider, and Sadler were all plucked off the scrap heap; the former two were both non-roster invitees to spring training, and Sadler was claimed off waivers from the Cubs last year. They may not have the pedigree, but the Mariners have helped each of them make the necessary adjustments to become key contributors to one of the best bullpens in the majors.