Two things we know to be true, as September threatens to turn into October:
- Bullpens matter so, so much in the playoffs, more than in the regular season, and:
- The bullpen you have now quite often bears little to no resemblance to the one you had in April.
Such is the life of the revolving bullpen door, where injuries, ineffectiveness and trades can mean a team cycles through dozens of relief arms each season, to the point that looking at season-long numbers holds relatively little predictive value. (Just ask your local Mariners, Cubs, Mets or Tigers fan how they feel about their relievers right now – despite relatively similar seasonal outcomes. We’re guessing you’d get some extremely varied responses.)
In that spirit, let’s look at four bullpens that might be trending into the playoffs just a little bit differently than you'd expect. If you’re wondering why the Padres aren’t here, it’s because the hardest-throwing bullpen we’ve ever seen is probably exactly as you’d expect, which is to say: elite.
Cubs
This is perhaps the most extreme example of the genre, because the first-half Chicago ‘pen was, to put it lightly, not scary. While the ERA was fine, the first-half Cubs relievers didn’t miss bats, with the fourth-weakest strikeout rate in the game. (Two of the three weaker teams were non-contenders in Colorado and Washington.) Strikeouts play in October, particularly out of the bullpen, and that simply wasn’t going to be good enough.
But fast-forward to the second half, and Chicago now has the fourth-best relief strikeout rate. After an unacceptably poor 19.2% K rate in April, we’re now looking at a massive 29.7% rate in September, which is a game-changing improvement – and a really difficult thing to do in-season.
There’s only one way to do that, really: Get some new arms. Of the eight members of the (domestic) Opening Day bullpen, only two (Brad Keller, Caleb Thielbar) are currently spending their days at Wrigley Field. (A third, Colin Rea, remains on the roster, but has spent most of his year in the rotation.)
Instead of Julian Merryweather (17% K rate), Ryan Pressly (15%), Chris Flexen (12%) and Nate Pearson (9%), there’s Andrew Kittredge (37.7% K rate as a Cub), Taylor Rogers (25.7%) and Drew Pomeranz (27.0%). While the loss of Daniel Palencia to a shoulder injury earlier this month hurts, he also made a Triple-A rehab appearance on Saturday and touched 100 mph while doing it. Keller, meanwhile, has quietly become one of the best relievers in baseball after mechanical changes helped provide a large velocity boost – and he’s gone from a 23% first-half strikeout rate to a 36% mark in the second half.
It’s a lot different than it was in April. There are new faces. Keller is better. Even Rea, unlikely to get a playoff start and potentially about to be a bullpen option, is coming off the best strikeout rate month of his career. Considering only those on the active roster, the Cubs bullpen has baseball’s best ERA, season-long, and also in September. The Cubs have some issues headed into October. This might not be one of them.
Mariners
Speaking of a bullpen that didn’t miss bats: Seattle relievers had the 29th-best strikeout rate in April, which is to say second-worst. In the second half, that’s ninth-best; in September, they’ve got the lowest walk rate of any bullpen, too.
Like the Cubs, there’s been some turnover here, as Opening Day relievers Collin Snider, Gregory Santos, Trent Thornton and Tayler Saucedo haven’t played large roles in recent weeks. That’s sort of a recurring theme, here: If the relievers you have aren’t getting the job done … get different relievers.
But unlike the Cubs, who made multiple moves to acquire veterans, most of Seattle’s improvement came internally. While Gabe Speier has been reliable all season long, Matt Brash didn’t make his debut until May, then upped his strikeout rate to 33% in the last two months after 26% in his first two months. (He has allowed more runs in the past two months – in part because the 19-game scoreless streak that started his season obviously couldn’t last forever.) Eduard Bazardo frankly wasn’t very good in April (16% K rate, 4.60 ERA); he’s evolved into one of the team’s more reliable relievers since, with a 1.26 ERA and 32.1% strikeout rate in the second half.
Seattle also has something that Chicago never did: one of the very few truly reliably elite relievers in the game in Andrés Muñoz, who has somehow upped his game in recent weeks. Muñoz, through the end of August, had a fantastic 31% strikeout rate. In his last eight outings, it’s 50%. It’s worth noting that he’s added three inches of break to his slider since July. This bullpen might not be as deep as others, but the top end is excellent.
Guardians
This shouldn’t make sense, but then again, little about the late-season Guardians makes sense. Relief ace Emmanuel Clase hasn’t been available since July, so the Cleveland bullpen has, of course, gone from ... fine in the first half (10th in ERA and K%) to fantastic in the second (third in ERA in K%), kicking it into an even higher gear in September, with a best-in-baseball 35.1% strikeout rate.
It’s hard to overstate how wild the names are here. Last year’s Big Four, the group that Stephen Vogt rode to the ALCS, consisted of Clase, Cade Smith, Hunter Gaddis and Tim Herrin. Smith remains elite, as he’s been since the moment he debuted, and Gaddis has been fine, if not quite as good as in 2024. But in addition to Clase being unavailable, Herrin has struggled badly down the stretch. Instead, these are the guys who've been the biggest (non-Smith) contributors:
- Matt Festa, acquired from Texas for cash on April 25 – who has nearly doubled his strikeout rate from the first half (18%) to the second (33%)
- Jakob Junis, a veteran swingman on his fifth team since 2021 – who has allowed just four earned runs in the second half
- Erik Sabrowski, a one-time Padres draftee and two-time Tommy John recipient who was claimed off waivers in 2021 after nearly quitting the sport – who made his season debut in late June and has somehow managed a 2.25 second-half ERA despite some truly massive walk issues
- Kolby Allard, the No. 14 overall pick by Atlanta a decade ago, who was designated for assignment by this very same Cleveland team as recently as “this July” – who, like everyone else, has massively increased his strikeout rate from 10% in the first half to 24% in the second
Even for a team that generally does not feature many household names, those aren't exactly household names. Cleveland never really does things the way you'd expect. It always, somehow, seems to work out.
Dodgers
OK, hear us out: You know the bullpen is a weakness. We know it, too. Everyone in the game does. And yet ... what is “a bullpen” anyway? If we’re getting into philosophical questions about how to define one of baseball’s oldest terms, you know we’re about to get weird, but the Dodgers are about to, too.
Let’s start with the obvious issues, here. The season-long ERA is bad (4.33, 21st), and the September mark is … considerably worse (5.69, 26th). It wouldn’t be the worst final month relief performance by a title winner, should they manage to win the World Series, but it would be in the bottom three, at least dating back to 1969. (What, you don’t remember the 2000 Yankees posting a 6.57 ERA out of the bullpen in September?)
This, obviously, does not fit into the spirit of the above “teams who are turning it on at the right time” category. Then again, look more closely at what’s happened in September.
To start with: Blake Treinen is doing something that has never* been done before.
*(back to 1912, when data is available, anyway.)
Not all of that damage was Treinen’s fault, to be fair. Two of those losses (Sept. 12 and 15) involved Treinen being charged with a loss in the 10th inning, thanks to the automatic runner scoring without Treinen himself allowing a baserunner. (In the first of those games, he retired the only batter he faced in the 10th before giving way to Tanner Scott, who later served up a walk-off grand slam.) But still, for as little as pitcher wins and losses matter … that’s still a lot of losses.
While Treinen may be on the playoff roster, it's easy to see him being dropped considerably down the pecking order. Without Treinen, that September bullpen ERA falls to 4.72. Without the injured Michael Kopech (6.75) and the ineffective Kirby Yates (7.71), it falls further, to 4.50. You see where we're going here; Scott will be on the roster, but there's not room for every underperforming-but-high-profile veteran.
Now, consider the reality that at least one, if not more, members of an overstuffed and high-performing starting rotation will find themselves in relief in the playoffs. Take Emmett Sheehan, who in his last five outings has a 1.15 ERA and a 42/7 K/BB ratio, yet almost certainly won’t be in the top three of the rotation. There is also whichever of Tyler Glasnow and Shohei Ohtani doesn’t join the obvious top two of Blake Snell and Yoshinobu Yamamoto.
Despite how badly the bullpen has pitched, the staff, as a whole, is trending towards the lowest average against in any month in baseball history. Remove some of the obvious veteran trouble spots, add some starters to the high-performing Alex Vesia and Jack Dreyer, and you might be stunned to see what this group actually can do in October. "The bullpen," as we know it now, may look extremely different when playoff rosters come out in a week.