Let’s begin with Jhoulys Chacin‘s projections from before the season.

As you can clearly see, RW23 — my own projection system — has been right on the nose so far when it comes to projecting Chacin, more so than the well-known projections systems of Steamer and ZiPS. And there’s a reason for that. There’s actually a big reason as to why Chacin has been so good in 2018. You can probably guess what that reason is based on the title of this post.That’s right. Chacin has stopped giving up home runs. Well, he’s still technically giving up home runs. He’s given up seven this season, in fact, but he’s been able to keep the ball in the yard better than almost every other starting major league pitcher.Here are the leaders of home-run-to-fly-ball percentage among qualified starters in 2017:

Only three pitchers with enough innings to qualify have allowed fewer home runs per fly ball than Chacin. The 30-year-old veteran is running his lowest HR/FB% since his last year with the Colorado Rockies in 2013. His ability to keep the ball in the yard is why his ERA and FIP look great, but also why his xFIP — which normalizes home runs based on fly ball rate — sits at a meaty 4.72.We can figure out why hitters aren’t connecting for home runs by simply looking at Chacin’s exit velocity on fly balls. As of July 1, that number is 90.7 mph, meaning the average fly ball hit off Chacin averages 90.7 mph off the bat. Only sixteen starting pitchers have done a better job at limiting hard contact on fly balls.This chart shows Chacin’s exit velocity on fly balls over the last three seasons, along with his HR/FB%.

This season isn’t even Chacin’s best when it comes to fly-ball exit velocity. That feat happened a year ago, though he somehow still managed to give up quite a bit more home runs than he has in 2018 thus far. And he was pitching in notorious pitcher-friendly Petco Park in San Diego! And therein lies the problem. Chacin is due for regression, and it’s quite possible that it will hit hard and hit fast.

As you already know, Chacin’s HR/FB% is the second lowest of his career. That’s good. His fly-ball percentage, though, is the highest of his career save for 2012 when he played at Coors Field. That’s bad. Here are those sentences in picture form.Chacin is allowing more fly balls than ever before, yet he’s giving up the fewest number of long balls of his career. That’s incredibly unsustainable. To make things even more confusing, his home stadium is Miller Park, a haven for home runs. But looking more closely at the numbers, it kind of makes sense in a way. Chacin has pitched a total of 97 innings, with 57.2 of those innings coming on the road. He’s thrown just 39.1 innings in homer-happy Miller Park. That, along with his low exit velocity, could explain why his HR/FB% is so low.

Except it doesn’t.

He’s giving up more fly balls at Miller Park than on the road but fewer home runs. Nothing about Chacin’s season makes sense, which is why what he’s doing won’t be able to last much longer.

Chacin has been a pleasant surprise for the Milwaukee Brewers, and he’s making those who clamored for the team to sign a high-profile pitcher this offseason look foolish. But unless the entire 2018 season is an outlier, Chacin just won’t be able to keep this up. I’m sorry to burst any bubbles, but despite his 3.71 ERA and equally strong 3.92 FIP, Chacin should be one of the reasons why general manager David Stearns should acquire pitching help before the trade deadline.