There ought to be no shame in a pitcher struggling at Coors Field. Many of the greatest pitchers on the planet have been humbled in that stadium and, last week, Stephen Strasburg became merely the latest among them. Allowing nine runs before being pulled in just the second inning, Strasburg posted what was far and away the worst performance of his career. He’d never previously given up more than seven runs in a game and his game score of 1 was not only his lowest mark ever, but is tied for seventh worst in baseball this season. Ideally, this could be written off as a Coors fluke for one of the game’s best pitchers, but instead it’s served to illuminate the frustrating reality that Strasburg has struggled mightily of late.

Over his last six outings, Strasburg has given up 26 runs in 30.2 innings pitched. Crunch the numbers and you’ll find that works out to a decidedly un-ace-like 7.63 ERA. These six outings have caused his season ERA to rise more than one full run, from 2.51 to 3.59. The good news is that there’s more than a little hope to be found in his peripheral stats. Over this awful stretch, his FIP is a massively more palatable 3.25, largely on the strength of a solid 29.1% strikeout rate and a roughly league-average 7.8% walk rate. It also likely won’t surprise you to learn that he’s posted an inflated .388 BABIP during this rough patch. Unfortunately, this is not to say Strasburg’s swoon has been entirely devoid of red flags.

In mid-June, Strasburg hit the disabled list with a back injury. Considering a back injury was the primary culprit in Strasburg’s first-half struggles last season, this latest DL stint was an unavoidably alarming development. Fortunately, he made a swift return to the mound. Any hopes that he’d escape the performance struggles which plagued him a year ago, however, have been derailed by his recent stretch. Whether those struggles are directly related to the injury is unknowable, but there are observable things about Strasburg which have changed since his return.

One of the more obvious changes has been the disintegration of his ground-ball rate. During the first half of the season, Strasburg posted a 44.4% ground-ball rate, which is almost precisely league average. In the second half, that rate has fallen all the way to 28.0%, which is tied for the third-lowest rate among 98 qualified starters.

The first place I looked for causes in a ground-ball rate drop that severe was pitch location. A logical working theory to start with for why a pitcher isn’t inducing grounders is that he’s not getting his pitches down in the zone and, as it turns out, this certainly appears to be the case for Strasburg. The images below generated by way of Baseball Savant show his pitch location prior to his mid-June DL stint (on the left) and since returning (on the right).

He’s living higher in the zone than he was before and, naturally, the key question is why? To answer this, one place to look is his pitches which typically work down in the zone such as his changeup and his curveball. Which brings us to another thing that’s changed about how Strasburg is pitching: he’s relying less heavily on his changeup.

Part of Strasburg’s brilliance is the quality of his pitch arsenal. He flummoxes batters with his mid-90s fastball and a one-two secondary punch with his changeup and curveball. And, for good measure, he’s also added a slider this year to encouraging results. But if any core pieces in his arsenal slip, it stands to reason that his overall effectiveness could slip as well.

Since returning from the DL, his velocity has been steady, with the notable exception that he’s lost a tick on his changeup. He’s also getting less drop and less run on the change. But, perhaps most alarmingly, has been the massive decline in results on the pitch that’s accompanied the slight drops in velocity and movement.

Strasburg’s Changeup Time Ball% Whiff/Swing GB/BIP 2013 42.9% 47.8% 66.0% 2014 34.6% 45.6% 60.0% 2015 42.3% 42.4% 49.0% 2016 pre-DL 37.3% 47.8% 73.3% 2016 post-DL 52.9% 36.1% 33.3% SOURCE: Brooks Baseball

Prior to the DL stint, Strasburg’s changeup was absolutely phenomenal. Those whiff/swing rates and grounders per ball in play (GB/BIP) rates were the highest of any of his pitches. Unsurprisingly, then, the change was Strasburg’s go-to secondary in two-strike counts. Since his return, however, he’s exhibited possibly less comfort and/or confidence with the pitch, cutting his usage of it nearly in half in those two-strike situations.

The good news is that this is not a universal decline across Strasburg’s arsenal. As the whiffs and grounders on his changeup have decreased, there’s been a concurrent increase in both of those categories on his curveball. This is what makes pitchers like Strasburg so dangerous: the diversity in his repertoire can help him compensate if and when he’s struggling with a particular pitch.

When analyzing short-lived struggles like the one in which Strasburg currently finds himself, the samples sizes are generally too small to generate straightforward “this is the problem and here’s the solution” conclusions. What I do find to be valuable takeaways instead are things to watch for going forward, and one of the things to watch is Strasburg’s changeup. It’s a feel pitch and there’s no reason right now to think he won’t get that feel back. Maybe it will happen in his next start or next month or in the postseason. When it does come along, the hope is that it will give him another weapon to command the bottom of the zone and push his ground-ball rates back up to normal. To state the obvious, the (all but certainly) postseason-bound Nationals could certainly stand to benefit from having their second ace return to top form before October.