If there has been one clear strength of the 2018 Phillies, it has been the pitching staff. The free agent acquisition of Jake Arrieta was a big part of turning the perception of the staff around too, and his All-Star-like performance over the first 2 months in Philly gave hope for a possible playoff run. Since the beginning of June however, Arrieta hasn’t been the same. Pivetta and Velasquez have had cold stretches, but it’s particularly concerning when involving a 32-year-old with a large contract. Is he on the decline? Is it just luck?

Many will argue Arrieta’s 6.66 (spooky) ERA in June relates to the defense behind him. Although the infield defense is a weakness for the Phillies, the high ERA does not account for unearned runs that Arrieta still did give up, and if you rarely miss bats and produce ground balls, you should expect to have errors behind you from time to time. Considering Arrieta’s 6.66 (double spooky) K/9 in June and a 2.45 HR/9 in June, the problem is certainly more than defense.

One thought about Arrieta’s recent struggles is that we should have expected this. He was outperforming his FIP, xFIP, and DRA in the first 2 months of the season. Through the end of May, Arrieta was posting a K% of 17.2%, and although he did a good job of controlling contact, a number that low rarely ends well. That is, if he can even continue to strike out that many with a whiff rate of only 7.2%, 3rd lowest among qualified starters. Arrieta wasn’t the All-Star his ERA suggested, but even then, his peripherals did not suggest a June this bad.

As you can see from the splits above, the biggest problem for Arrieta this month seems to be how well the contact-controller is controlling contact. The huge increase in home runs probably is a result of small sample size and the bad luck of a 26.9% HR/FB%, but even then, it is clear he is not doing well in that department.

You would expect from the home run numbers that Arrieta has been allowing more fly balls and less ground balls, which is true, but only to a minuscule extent. He has not produced as many grounders as somebody with his lack of strikeouts, but has still produced over 50% grounders in June.

Looking further into each month’s fly ball splits, one thing is clear, and that is a majority of balls in the air given up by Arrieta have been hit hard, at least as of late. Even though it still seems like bad luck that got him at 2.45 HR/9, especially considering how many are still being hit to opposite field, the problem is clear. One question you may have when looking at these splits is, if the peripherals from May to June are that consistent, how come he was so good in May and so bad in June? That’s when small sample size, and largely luck comes into play. In reality, Arrieta’s skill level is probably between the ERA of May and June. Although we have concluded that giving up hard hit fly balls has led to a problematic ERA in June, we still have not uncovered why more balls are being hit hard.

Maybe there is a change in approach that is causing this. Arrieta increased the usage rate of his slider from 9.44% in April all the way to 23.9% in June, while steadily decreasing the usage of his sinker. While maybe this is the concern, Arrieta’s slider has been one of his best pitches at reducing power and producing grounders. Maybe we should look further into which pitches are giving up more extra-base hits:

Oh wow. That’ll do it. Although there are slight increases in other pitches (possibly do to reducing to the mean), it’s pretty clear that Arrieta has given up too many bombs on curves. This isn’t a situation where Arrieta has only thrown the curve ball a couple times either, he uses the pitch around 12% of the time. On the bright side, it seems like a pretty minor problem given the possibilities. A low usage pitch is getting hung too often over the course of a month, something entirely fixable, considering he’s had this problem before with other pitches.

To look further into why his curve is struggling, as the Phillies broadcast has theorized, it’s related to a loss of control. While the velocity and movement of his curve ball has stayed relatively consistent throughout each month of the season, the location has not.

As you can see, in the first 2 months of the season, Arrieta managed to bury his curve ball in the bottom of the zone, inside to lefties and outside to righties.

In June, it has been a different story. Arrieta has left it over the heart of the plate way too often, to both lefties and righties. That is entirely way too dangerous, and it’s easy to see why home runs have become a problem for the former Cy Young winner.

Looking even further into it, we can see why Arrieta has struggled to command his curve ball. The lower release point has caused him to get under the curve, which allows hitters to get under it as well. The release point that Arrieta had on his curve ball was the lowest release point over a full month he’s had on the pitch since 2012, and he was not good in 2012. It’s not particularly concerning for the long-term, as Arrieta has had months in the past where his vertical release point has been off, and he has fixed it relatively quickly every time.

To sum it all up, Arrieta’s struggles have been partly luck, and partly loss of command in his curve ball. Overall, his poor and spooky June numbers do not point to his inevitable decline, at least not yet. Chances are he fixes these issues in no time and gets back to being a mid-rotation starter as the Phillies’ deep rotation gets set for a playoff race.

Stats and graphs provided by Fangraphs.com and Brooksbaseball.com