The Mariners aren’t the first team built on a run differential-beating bullpen

Can teams be built to cheat probability? Seattle’s league-leading 15 victories in one-run games has felt like the story of the season. The spectacular late-game heroism has been bad for my heart rate and sleep schedule, but excellent for Seattle’s playoff chances. If Seattle were to simply go .500 for the remainder of the season they’d earn 87-88 wins, likely enough to earn a Wild Card spot in a top-heavy American League. They must get more out of their offense, but right now they’re surviving by the dominance of their bullpen. That’s a style of victory we’ve seen elude the expectations of Pythagoras before.

Through Tuesday morning the Mariners rank 8^th in Bullpen ERA, as well as 7^th by FIP and 4^th by fWAR. It’s been surreal to see Seattle amidst the “elite” of the AL in the standings, but elite is exactly how the Mariners’ bullpen should be described based on their peripherals thus far. Just the Yankees and Astros lead Seattle by K-BB%, and both the addition of Álex Colomé and recent mechanical improvement of Juan Nicasio should only further solidify the back end. It’s that brilliance that could allow the Mariners to finally bring the playoff rains to the Pacific Northwest.

These Mariners have been remarkable escape artists, but they’re following a deer trail many teams have tread to avoid the precipice of expected win/loss. Over the past 30 years, 18 teams have maintained a winning percentage of .650 or better in one-run games over a full season, and it’s only become more common as teams have leaned more heavily on their bullpens.

By and large, the teams who have best exceeded their run differential and excelled in one-run games have been those with dominant results from their bullpens. A few outliers exist, like the infamous 2016 Rangers and the otherwise-terrible 2012 Cleveland, but most teams who rank poorly on the whole have individual dominance to thank. The 2002-2004 Dodgers were privy to perhaps the most dominant three-year stretch of any individual reliever in prime Eric Gagne, which meant any late-inning lead was a lock. Similarly, the Yankees frequent this list despite sub-elite bullpens overall thanks to Mariano Rivera and various strong setup men.

Prior to the acquisition of Colomé, Seattle seemed to fall in that second outlier group. They boasted a lights-out closer and some good setup options, but saw their overall numbers dragged down by the innings-eaters in games that the starters failed to keep within reach to begin with. Now, however, Seattle is rolling with a healthy Ryan Cook, a refined James Pazos, and a no-longer-a-Met Chasen Bradford, Seattle has three decent options middle/long relief options, as well as Marc Rzepczynski. With a high leverage group of Nicasio, Colomé, a soon-to-return Nick Vincent, and of course Edwin Díaz, nearly every lead is safe, and small deficits can remain within reach.

Bullpens are, by their small sample nature, volatile. This could fall apart numerous ways, including injury, bad luck, or simple ineffectiveness. But while the Mariners pathway to victory so far has been atypical, it’s far from unprecedented. If the Mariners make the playoffs this year, it will be the most stressful style of baseball imaginable, but they’re built, in theory, to sustain it.

I’m just sure not we are.