There are many varieties of closers but only two types of good ones: closers who can reliably save a game and closers who devour the hearts of lineups.
The former is well and fine; Cleveland rarely griped about Cody Allen working the ninth inning, for instance. Yet there's a reason why the Indians shipped a freight of prospects to New York for Andrew Miller. Miller and his ilk—Zach Britton, Aroldis Chapman, Kenley Jansen, Dellin Betances, and that may be the entire list—go about their work in a way that is perfomative as much as it is functional. They run out of the bullpen as bipedal of embodiments of impending doom, throwing signature pitches so famously dominant that they are characters unto themselves. Facing them means you are completely, utterly, summarily fucked.
Needless to say, there are not many pitchers like this. The big-ticket trades for Miller, Chapman, and the at-least-temporarily-no-longer-unhittable Craig Kimbrel within the past year reaffirms them as extremely valued currency. There's no exact science for minting them, either. Chapman was a massive Cuban import. Britton, Betances, and Miller were failed starters. Jansen is a converted catcher.
And then there's Seattle's Edwin Diaz, who for the purposes of this exercise exists in a sort of liminal space. Diaz was a starter until May, when the Mariners, citing his lack of a third pitch, announced they were converting him to relief in order to maximize his long-term potential. Within a month, he was on the big club and thus began a run of pitching so stupefying that it transcends the usual caveats of length. It borders, quite literally, on reliever perfection. But Diaz has thrown only 39 innings in the majors, a thimble-sized sample—still too little to lump him in with pitchers who have been at this for multiple seasons without interruption.
In those 39 innings, Diaz has a 2.28 FIP and 2.02 xFIP. He struck out 70 batters, good for a K rate of 16.15 per nine innings. This may not be totally sustainable, in the same way that Usain Bolt can't sprint at top speed for a full 200 meters and Steph Curry cannot hit every single three-point attempt. But among major leaguers with at least 30 innings pitched, only Betances (15.51 K/9) is within striking distance. Miller, who sits in third place, is more than a strikeout-per-nine behind him.
Here is the most telling stat of all: in those 39 short innings, Diaz's 1.2 fWAR ranks 16th among all Mariners relievers since 2000. This is mostly attributable to his being a fencepost-thin 22-year-old with an archetypical fastball-power slider combo, but it also speaks to the context of the organization he pitches for. Talent like Diaz's would stand out anywhere but it gleams especially bright in Seattle, which since the turn of the century has enjoyed ace pitching (Felix Hernandez) and star hitting (Ichiro, among others) but rarely a watertight relief corps.
There have been exceptions, of course. The quietly indefatigable Arthur Rhodes stacked up 8.5 fWAR over 312 appearances. Kaz Sasaki gave them four years of split-fingered goofiness in the ninth inning. The Mariners enjoyed J.J. Putz's great years and Rafael Soriano's peak. Shigetoshi Hasagawa stuck around for a while and was mostly pretty fine. The now anonymous Danny Farquhar turned in a delightful 2014 season, 13 years after Norm Charlton dazzled in his final MLB campaign. Most recently, Seattle turned the neat trick of excavating Tom Wilhelmsen, a 27-year-old who once quit baseball to tend bar, and molding him into a workhorse reliever. (Before the season, they flipped him to Texas for a starting center fielder, and then reabsorbed Wilhelmsen back into the fold seven months later.)
And so on. They all sufficed to varying degrees but Diaz, in aesthetics and results, has reached heights in three months that, collectively, none of them so much as scraped over a decade and a half. It means more for Diaz to sizzle in Seattle than it does for Betances in New York, what with Miller and Chapman and David Robertson all excelling in the wake of Mariano Rivera's retirement. General Manager Jerry DiPoto's early optimism notwithstanding, there was scant reason to expect this from Diaz, and certainly not so soon. Now it could be the status quo for a decade.
Diaz's rise fits a wider American League West pattern of teams finally quenching long-held positional thirsts. Cliff Lee deployed his unique brand of needlepoint pitching for four teams but nowhere was its impact more heartfelt than in Texas, which hadn't employed a legitimate ace since 40-something Nolan Ryan. The Angels spent decades lusting for a legitimate superstar—the best player on their 2002 World Series winner was David Eckstein, because of course—and wound up drafting Mike Trout, who could end his career as the greatest player in history. The Astros churned out All-Star infielders dating back to the Killer B's era, but never a shortstop better than the toothless Adam Everett. Now, they have Carlos Correa, whose first two seasons portend a Hall of Fame career.
In Diaz, the Mariners have solved their bullpen with a pitcher who could become the most dominant reliever in the game. It's still early, but the Mariners probably feel those 39 innings are long overdue.
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