A little more than two months ago, I noted that the Mariners’ bullpen had been — through that point in the season — among the most improved in the game, relative to preseason expectations. Before the 2018 season began, we projected Seattle relievers to strike out 9.1 batters per nine innings and walk 3.5.
A couple weeks into the season, they weren’t doing that. They were performing much better than that, actually. At the time I wrote that first article, Mariners relievers had struck out 10.7 batters per nine innings and walked just 1.5, both of which were tremendously good numbers and perhaps merited further investigation at the time. But it was still early, so I kept the article general and cautioned that we shouldn’t necessarily expect the men in teal to keep up their early-season performance too much longer.
Well, we’re now more than a third of the way through the major-league schedule, and the Seattle bullpen has stayed improved. In fact, the Seattle bullpen has been among the top three or four in the game, no matter which way you slice it, but this piece is about improvement against expectations. Here’s an updated version of a chart I included in my original article, which plots each teams’ actual relief K/9 and BB/9 (adjusted so that positive figures are good in both cases), through games played on Friday, against our preseason expectations of the same:

Observant readers will note that there is another happy story to tell here about the Astros’ pen — featuring Héctor Rondón and Chris Devenski — and a sad one about the Orioles, featuring almost every Oriole. But, again, this article is about the Mariners, whose improvement relative to projections in both K/9 and BB/9 has been outstanding — and key to the club’s outrageous performance in one-run games, which was detailed here by my colleague Jay Jaffe. Maybe it’s finally time to dive a little bit deeper into what they’ve been doing and why it’s been successful.
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