Gray has a fastball that can zoom above 95 mph, but the slider has been the "out" pitch for 81 of his 129 strikeouts, according to Statcast™ data. So he was doomed without it the last two starts. The problems were different: against the Marlins he threw it at 90.49 mph, or in the range that it works; against the Phillies it looped in at 87.43.
"Against the Marlins, the action was so bad, really bad," Gray said. "It was really flat. It didn't have an effect at all. It was an easy, hittable pitch. The one [Giancarlo Stanton] hit [for a fourth-inning, two-run homer] was a terrible slider. I don't think I threw any good ones that day. Zero."
Against the Phillies, his attempt to manufacture the needed downward action led to tentative deliveries.
"I had some really good ones -- a groundball double play out of one, a swinging bunt when the guy got on with another -- but I didn't feel it was punch-out material," Gray said. "Beating them in the zone down is where you get your swings. I knew I had to get my slider back to where it was before.
"Once I get the right movement back, I can throw it however hard I want to. It's just the hand positioning and rotation that I need to crack down on."
Gray also said he believes his body language gave away some pitches. What's important is in the days between starts, Gray went from knowing he needed to be better to knowing how to do it.
"To see why you're having a little bit of trouble, attack it and see results -- I threw a really good bullpen yesterday with a lot of good sliders -- as long as I take it to the mound tomorrow it's going to be good," Gray said.
Thomas Harding has covered the Rockies since 2000, and for MLB.com since 2002. Follow him on Twitter @harding_at_mlb, listen to podcasts and like his Facebook page. This story was not subject to the approval of Major League Baseball or its clubs.