When Jake Arrieta made his 2017 season debut, he raised a certain amount of alarm. Although he held the Cardinals to all of one single unearned run over six innings, his velocity was sharply down, and that never escapes an analyst’s notice. Arrieta, therefore, was immediately put on the watch list. The reasons, I’d say, were justifiable.

Arrieta just made his eighth start. As with his first, this one came in St. Louis. The good news? His velocity is coming back. Compared to that first game, Arrieta’s sinker bumped up by a tick and a half. The same thing happened with his curveball. His cutter jumped up even more. Joe Maddon said before he wasn’t worried about Arrieta’s zip, and now we’re seeing some more familiar readings. So much for that early-season panic.

Yet now there’s different early-season panic. Through his first eight games a year ago, Arrieta allowed a combined nine runs. This year, he’s allowed a combined 33. Arrieta’s sitting on a worse ERA than Jhoulys Chacin, and with the Cubs a game under .500, this, too, can’t escape notice. Arrieta doesn’t look like himself.

Anyone who’s been paying attention knows that it’s not like some switch just flipped. If any switch flipped, it happened last year, when Arrieta started to get worse and worse as the days rolled by. At no point was Arrieta a true liability, but in retrospect, his days of pitching like an ace were rather brief. Arrieta, before, reached heights like few others have. There’s reason to wonder now whether Arrieta might ever again resemble that kind of weapon.

Let’s get into this. Arrieta’s issue in last year’s second half was one of location. His mechanics started to go awry, and his pitches would drift on him. Comparing this year to later last year, Arrieta now is throwing more strikes. His walks are down, and his strikeouts are up. Both of those things are good. This is a different sort of struggle. It’s more of a contact-management struggle, actually.

Here’s one good way to visualize that. Behold a rolling-average plot of Arrieta’s ground-ball rates over time:

Arrieta the Cub has been a ground-ball pitcher. He’s also been a strikeout pitcher, and a low-hit pitcher, but along the way, he’s consistently turned more than half of all the balls in play into grounders. You see that spike at nearly 70%. That didn’t reflect Arrieta’s true talent, but hitters couldn’t do anything. So far this season, grounders haven’t been there. Arrieta has one of the very biggest declines in grounder rate around, and this is a partial explanation for why he’s already allowed eight homers. Last year, he allowed 16; the year before that, he somehow allowed just 10.

As a related matter, Arrieta hasn’t been able to count on his cutter like he could in his prime. When a pitcher gets worse, the pitcher tends to get worse across the board, but a good way to understand what’s happened with Arrieta is by understanding that his cutter has left him. He still throws it, fairly regularly, but now check out this other rolling-average plot, showing cutter run values above or below average:

In 2015, no pitcher threw a more valuable slider or cutter. This year, no pitcher has thrown a less valuable slider or cutter. There was a transition phase — Arrieta’s 2016 cutter, overall, was neither good nor bad. But this year, it’s been a real problem. It’s not a full explanation of Arrieta’s issues, but rather a symptom. Something is off, which is knocking his pitches off, and when you chip away at any repertoire, the result is certain to be negative.

I don’t know if I can identify the root cause. However, I think it’s possible, and to start toward that end, I’d like to borrow an image from Brooks Baseball. This shows Arrieta’s average horizontal release points since 2014.

There’s been a shift there, toward third base. Nothing dramatic, but definitely something. And so now it’s time to look at some pitches. First, two pitches from earlier last season. Then, two pitches from this past weekend. Don’t worry if you don’t know what to look for, because I’m also going to throw in some screenshots.

Arrieta, 2016

Arrieta, 2016

Arrieta, 2017

Arrieta, 2017

What I’m targeting is Arrieta’s front foot. Screenshots, with last year’s pitches on top:

And, in case you’d prefer, here are the same two bottom screenshots, but with the top screenshots replaced by images from 2015, when Arrieta was even better:

Part of the narrative when Arrieta took off post-trade was that, unlike the Orioles, the Cubs didn’t mind that Arrieta wanted to throw across his body. Classic pitching mechanics involve a step toward home plate, almost in a line. That way, everything’s in alignment and your body doesn’t get in its own way in terms of pitching the ball forward. Not every pitcher looks like the classic, ideal pitcher, and Arrieta just wanted to throw the way he’d always thrown. The Cubs let him, and Arrieta became great. At times, he was almost literally unhittable.

What I think could be a problem now is that Arrieta is pitching too much across his body. As always, I need to make sure you understand I don’t know this to be a fact. He could have any number of other issues. But compare the positions of his feet. It’s easy to see that Arrieta’s throwing across his body in all of those pictures, but if you look at things two-dimensionally, in the more recent pictures, Arrieta’s front foot is more to the right, away from the rubber. There’s a larger visible gap between Arrieta’s feet. There’s just the slightest amount of distortion because the 2017 pictures are slightly zoomed in, but I don’t think that’s it. I think Arrieta’s stepping too far out of even his own alignment, and that would explain the horizontal release-point shift. It could also explain worse location, flatter pitches, reduced velocity — really, it could explain anything and everything. When mechanics go off track, the pitcher isn’t the same pitcher.

The good news here is that, by and large, Arrieta looks like a similar guy. He’s got basically the same pitches, and basically the same mechanical quirks. I’m less concerned about his velocity than I used to be, and if you look at his exit velocities, they’re still strong, and better than last season. Arrieta has pitched better than his current ERA, and I think this all should be fixable. But, the absent grounders are one sure sign of something being off. Seems to me, the solution could lie within Arrieta’s stride. If he finds his alignment, he should again be awfully good. Whether he gets there, well, that part’s not really up to me.