A well-placed landmark sign might inform gawkers that Kimbrel also posted the first such season in 2012.
Lowering the minimum, only Aroldis Chapman's late-starting, 54-inning 2014 season has crossed the threshold. Outside of that, no one else has touched 50 percent in a season of even 30 innings (Carter Capps came closest, in 31 innings in '15). Before Kimbrel came along, the most dominant strikeout rate season on record belonged to Dodgers closer Eric Gagne, who fanned 44.8 percent of hitters during his historic 2003 season.
Despite the steady rise of strikeouts in the game, strikeout-percentage kings are not regularly toppled. Gagne's mark has still not been beaten by anyone not named Kimbrel or Chapman (who only did so in that 2014 season). Gagne took the throne from longtime Astros closer Billy Wagner, who first wrestled it from early 1990s Reds fireballer Rob Dibble in '98 by whiffing 39.3 percent of his challengers.
The top of this leaderboard unsurprisingly tracks the rise of the single-inning reliever. The strikeout-percentage record was once shared by starter Dwight Gooden's 218-inning 1984 season and Hall of Fame fireman Bruce Sutter's 1977 campaign (107 1/3 innings). The number that put them atop the all-time list back then, 31.4 percent, would ranks 19th among pitchers meeting the 60-inning minimum in 2017, tied with Brewers reliever Anthony Swarzak.
While the bar for strikeout dominance has risen precipitously, Kimbrel has found a way to vault clear over it. His is a simple-but-effective formula. He whips a 98.3-mph four-seamer, and plays off it with a deadly curveball that comes in at a ridiculous 87.3 mph, on average. Especially once he gets ahead in the count, Kimbrel throws the heaters up high and buries the curves low or completely out of the zone.
Through some combination of velocity, deception and sequencing -- and maybe a little intimidation from his condor-like stare-in -- Kimbrel befuddles hitters. They have missed on more than a third of their swings at pitches inside the strike zone this year -- the highest rate against any hurler with 250 in-zone pitches. Outside the zone, they miss on 62.4 percent of their swings -- also tops against any pitcher with 150 such pitches.
With that type of pure stuff, strikeouts are naturally going to pile up. But there are other relievers with incredible out pitches. The thing separating Kimbrel from the pack -- and even from other versions of himself -- seems to be the frequency with which he's able to deploy his.
Kimbrel is taking hitters to two-strike counts 78 percent of the time -- 184 of the 236 he's faced. It would be the highest such rate in a 60-frame season since complete count record-keeping began in 1988.
In particular, Kimbrel is reaching 0-2 counts. During his 2012 season, Kimbrel put 43.3 percent of his batters in an 0-2 hole -- a clip that hasn't been matched since. This year, he's returned to that neighborhood, taking 35.2 percent of plate appearances to 0-2. Just last year, he did it only 26.4 percent of the time. That may not sound like the biggest difference, but spread over 236 batters (his 2017 total), the improvement amounts to 20 additional hitters almost destined for a slow walk back to the dugout. Yankees setup man Dellin Betances, for instance, boasts similarly filthy pitches but takes only 25.7 percent of his batters to 0-2.
The result of Kimbrel putting his weapons to use in advantageous counts is his second serious entry into the race for the greatest relief season. He will notch more total strikeouts than some qualified starting pitchers, and leave perhaps the most extreme artifact yet of the ongoing struggle between hard-swinging hitters and overwhelming pitchers. The bar for any current or future relief ace hoping to call himself the strikeout percentage king will, once again, be raised.