Since its inception in 1995, pitching at Coors Field has been one of baseball’s biggest mysteries. The Colorado Rockies have tried humidors, four-man rotations, and countless other tweaks, but have not been able to solve their biggest deterrent to winning: a competent pitching staff. According to ERA-, they have fielded an above average pitching staff in just seven of their 24 season in existence. No matter what they try, they have not been able to figure out how to pitch effectively at altitude.
Until now, perhaps. In an admittedly small sample, Rockies righthander Jon Gray has limited opponents to a 2.99 ERA and 0.82 WHIP in his last five home starts. He has 35 strikeouts to six walks during this stretch, a 33 1/3 inning sample that normally would not warrant a full breakdown of why it was so great. However, Jon Gray pitching at Coors Field has much bigger ramifications than just about any other pitcher-ballpark combination in baseball, so even relatively small samples of extreme success are of interest.
Gray’s position within the Rockies organization is unique. As a former first round pick and the first of several promising young arms to make their way through the Rockies’ pipeline, he's the first (and so far, best) attempt for their recent "Can pitching work at Coors Field?" experiment. Their prior plan of fielding a staff of ground ball pitchers didn't pay off, so they took to acquiring as many power arms as possible in recent seasons. After all, if a pitcher with a mid-90s fastball and wipeout slider can’t get hitters out at altitude, who can?
Let’s focus on that slider, though. Gray has been throwing it more often as the season goes on, topping out at a 35 percent usage rate in June before tapering off slightly in his first three July starts.
Opponents swing and miss on his slider at a 25.9 percent rate, and are batting just .172 and slugging .238 when they do make contact. According to FanGraphs’ pitch values, it has been one of the top 10 sliders in baseball (per 100 pitches thrown). It has gotten better throughout the year as well. Opponents hit .211 off the slider in two April starts, .161 in May, and .130 in June before a bit of BABIP regression in July.
Here’s where it gets interesting: Gray has demonstrated a measurable uptick in slider velocity as the season has gone on. In April, the slider averaged 88.2 miles per hour and topped out at 90.6 mph. May and June brought with them small increases in velocity. Now in July, Gray is averaging 90.4 mph with his slider and has gotten has high as 93.8 mph.
As you might expect, Gray has lost a bit of movement on the slider as it has added velocity. His horizontal movement on the pitch has tapered off as velocity has increased, and vertical movement has largely held steady. While his slider still has plenty of bite, it is almost behaving more like a cutter, and Gray is even using it as such. He is throwing it inside against lefties a bit more often, a trend we have seen other pitchers (including Detroit’s Jordan Zimmermann) utilize to great effect this season.
There are a number of different reasons why Gray is throwing his slider harder, but one possible explanation is velocity separation between his pitches. Gray touched on that idea — and potentially hinted at what was to come — when speaking with FanGraphs’ David Laurila in early June.
"I think the curveball is a better separation pitch for me than the changeup. I think it has a better chance to miss bats, because it has a lot more movement. My curveball is more of a finesse thing, but it’s still been a huge weapon the last couple of weeks. I can steal strikes with it and dip it on the plate."
When Gray throws his slider harder, he creates less separation between his slider and fastball, but creates more separation between those two pitches and his curveball, which has averaged 78.3 miles per hour this season. Gray doesn’t throw the curve much, but when opposing hitters are gearing up for either a fastball or slider, he makes them look like this (even when they are named Freddie Freeman).
A second, and perhaps more important reason for throwing the slider harder may be due to how the pitch performs at altitude. Looking back at Gray’s slider velocity plotted on a per-game basis, we see the two highest peaks occur in his last two home starts. Over the years, PitchFX data have revealed that sliders and cutters are among the most effective pitches thrown at Coors Field, and could work well when paired with a power fastball.
Obviously, it’s far too early to conclude that Gray has solved the Rockies’ age-old problem of pitching at Coors Field. This entire thought experiment is predicated on five starts’ worth of success (against lackluster offenses, no less) and includes fewer than 100 innings of data. However, the little anecdotal evidence we have suggests that there might be something here, and for a franchise that has struggled to pitch in its own ballpark for so long, might be worth latching onto so long as their young starter continues to rack up strikeouts.
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Rob Rogacki is a contributor at Beyond the Box Score and the Managing Editor of Bless You Boys, SB Nation's Detroit Tigers community. You can follow him on Twitter at @BYBRob.