Rockies’ Jon Gray has his slider back

August was not kind to Jon Gray. After taking down the Dodgers on Aug. 2, Gray had a 3.77 ERA with a 120:37 strikeout-to-walk ratio in 114 ²⁄₃ innings. Opponents were batting .223/.299/.369 against him—roughly the season of Alcides Escobar. In seven starts from August 7 to September 10, he put up a 7.71 ERA with a 36:16 K/BB in 35 innings. Opponents hit .310/.382/.448 off him in that stretch—roughly the season of Dustin Pedroia. People were concerned. Was Gray breaking down after a long season? Or were we witnessing another Rockies pitching prospect bust?

Then, on September 17, Jon Gray turned in the best start in franchise history. Like much of his record setting rookie campaign, the story of Jon Gray’s dominant performance against the Padres starts and ends with his slider.

The slider has been not only the most effective pitch in Jon Gray’s arsenal, but one of the most dominant pitches in the majors this season. According to FanGraphs’ pitch values (which seeks to help answer the question "How well has a pitcher performed using a certain pitch?"), Gray’s slider sits just behind that of José Fernandez and Clayton Kershaw but just ahead of Madison Bumgarner and Chris Sale.

But back in August, during his stretch of bad starts, he was struggling to command the pitch. Usually Jon Gray will throw his slider about 26 percent of the time while relying primarily on his mid-to-high 90’s fastball (50% of his pitches) and using his curveball (11%) and change up (7%) to set up the rest. As he gets ahead in the count, however, Gray uses the slider to generate swings (68% swing rate) and misses (28% swing-and-miss). When he gets up to two strikes on a batter, the slider becomes a deadly out pitch, which he uses 41% of the time. While he was struggling, he was getting fewer swings—and, ipso facto, fewer whiffs—which limited his ability to use the slider. On September 10 against the lowly Padres, he didn’t have a single pitch generate more than 15 percent swings and misses. For a strikeout pitcher like Jon Gray, that’s bad news. Gray was a strikeout pitcher on Saturday, and this should give you an idea why.

The first slider he threw was in an 0-2 count to Luis Sardinas with one out in the first. Gray had started him off with a 95 mph fastball for a called strike, followed by a 79 mph curve for another called strike. He was commanding the zone. You have to think Sardinas knew what was coming, yet he seemed powerless to do anything about it:

That is the template for Jon Gray’s success: throw the fastball for strikes, surprise them with the curveball occasionally, and finish them with a slider. And he worked this template over and over again to Padres hitters, who are 29th in the bigs with a 25 percent strikeout rate. Look at what Gray did to Orlando Arcia in the top of the second, who was so embarrassed apparently he thought that strikeout was worth two outs and the inning was over:

Wil Myers promptly excused himself from the proceedings after this one.

And, despite swinging at the pitch, Ryan Schrimpf seemed to disbelieve what just happened.

How about the bite on this one to Alexi Amarista in the fifth?

Really, this was as close as the Padres got to touching Gray all night:

Perhaps the most crucial at-bat for Gray, the one that showed how far he’d come from his struggles a month prior, came in a protracted battle with Arcia, the Padres’ right fielder. Arcia stepped to the plate in the top of the seventh with one out. Gray had already struck out 13 batters at this point, one short of tying the Rockies record. He started Arcia off with a 96 mph fastball for a called strike, then made him look absolutely foolish by getting him to swing at a 79 mph curve. Gray and catcher Tom Murphy decided to go for his second strikeout on the curve, but it missed outside. Arcia and Gray both knew what was next, but the slider also missed just off the plate. Arcia fouled off a 96 mph fastball to stay alive. Then, in perhaps the only moment Gray got squeezed all night, the umpire called the 88 mph slider a ball, low and away. With the count full, Gray knew he needed to get the one in for a strike, or at least one that looked like a strike. He’d done it all night. He reached back and unleashed a 92 mph slider that would get him tried for witchcraft in 17th century Salem.

On Saturday, Gray threw his slider 26 times, 20 times for a strike. Nineteen of those sliders came in two-strike counts, and he generated an absurd 56 percent whiff rate on the pitch. In all, 12 of his 16 strikeouts came on the slider.

Jon Gray might never pitch a better game for the rest of his career. He pounded the zone early and often (72 of 113 pitches for strikes), commanding his fastball and mixing in his (new) curveball. This allowed him to unleash a pitch that just may just dominate the rest of the league for years to come.