The consistency of Christian Yelich throughout his first three major-league seasons, each with identical wRC+ figures of 118, was both promising and, in some ways, perhaps maddening. On the one hand, a hitter with a 118 wRC+ is a good hitter. Especially at such a young age. On the other hand, Yelich has been a ground-ball machine, and with his 6-foot-4 frame, the adjustment to bump up the production a few ticks has seemed so obvious. He doesn’t have to be a slap hitter, and yet he largely has been. And, as with Kansas City’s Eric Hosmer, that inability to adjust — to hit the ball in the air with even slightly greater frequency — has been somewhat confounding.

Unlike Hosmer, Yelich has taken a step forward this year. Our own Jeff Sullivan took early notice of some changes back in May. Yelich was laying off low fastballs, getting himself more good pitches to hit. He was doing a better job of turning on the inside pitch, and a better job of using those offerings to create loft. For the year, Yelich has dropped his ground-ball rate by six points, and while that’s one of the larger decreases across the game, Yelich’s still putting the ball on the ground more than almost anyone.

But then this past week, Yelich showed something else new. You’ll be able to see it rather clearly in this image. Yelich’s already doubled his career-high in home runs, with 18. Here’s the first 15, from before last week, and then you’ll see three new ones pop up in the week since:

It’s easy to spot. In the first 457 games of his career, Yelich hit four home runs to the opposite field. In his last eight games, he’s tacked on three more. The uptick in his power production, on a whole, is obvious. It’s right there in the home-run totals. Last year, Yelich hit for as much power as Anthony Gose and Kevin Pillar. This year, he’s hit for as much power as Carlos Correa and Justin Upton. His 69-point increase in isolated slugging percentage ranks 10th among 92 qualified batters from last year to the next. On the surface, changes in power production are always clear to spot. Where they’re coming from is sometimes less clear.

Christian Yelich Power Output by Direction Direction Pre-2016 2016 ISO Increase Pull .111 .187 68% Center .169 .239 41% Opposite .167 .318 90%

As evidenced (and helped) by last week’s stretch, the brunt of Yelich’s power uptick has come in the opposite field, where his ISO has nearly doubled from where it was the previous three seasons.

His manager, Don Mattingly, hints at a more versatile range of bat paths. “Watching him hit from the other side a few years back, I’ve always seen a really good swing,” Mattingly said before a recent game in Cleveland. “And I think he’s a guy who’s just now starting to get the barrel in different angles.”

Yelich, as my colleague David Laurila pointed out last month, is particularly cagey when discussing the more granular aspects of his game, but Mattingly’s comments are borne out in the video. Consider Yelich’s swing on one of those opposite-field homers from last week, which came against a changeup located low-and-away (Zone 13 in BaseballSavant’s strike zone box):

And then consider a swing from last year, also on a changeup, also located in Zone 13:

The two pitches aren’t identical — no two are — but more importantly, neither are the swings. Like so many hitters across the league this season, Yelich now features a more exaggerated leg kick, giving his swing more rhythm — and a lower starting position with his hands, helping create a swing plane better designed to drive the ball in the air with authority. These two, cherry-picked swings can’t be taken as perfect representations of Yelich’s go-to approaches, but you see the way he chopped down at that pitch last year, and the way he got under a similar pitch this year and caught it square in its flight path. Like Mattingly said, he’s learning new angles with the barrel.

But what’s perhaps more interesting about the new angles Yelich has learned are the angles Yelich hasn’t yet learned.

“I still think there’s room for him to grow,” Mattingly explained. “He still hasn’t really truly learned how to pull the ball. When he learns how to pull the ball, he’s going to be really scary. Because they’re not going to be able to do some of the things they do to get him out now when he finds that next angle. Once he gets that next piece in there, he’s going to be one of the best hitters in the game.”

Mattingly’s absolutely right that, if Yelich finds another piece, he could legitimately become one of baseball’s most dangerous hitters. He’s already 23rd on this year’s wRC+ leaderboard, creeping up on Paul Goldschmidt and Edwin Encarnacion. Mattingly’s absolutely right that Yelich still has room to grow, even despite the growth he’s already shown this year. And that’s because Mattingly’s absolutely right that Yelich still hasn’t truly learned to pull the ball.

Lowest pull-field wRC+, 2013-16, min. 250 balls in play

For his career, Yelich’s pull-field wRC+ is 75. This year, it’s up to only 84. Strides have been made, overall, but they haven’t been in the pull-field department. And here’s where Mattingly’s gaudy claims are validated: when Yelich pulls the ball in the air, he’s done it with an average exit velocity higher than almost anyone. When he pulls the ball in the air, he’s hit it farther than almost anyone. Yelich’s pulled air balls have truly been elite. They’ve also been fleeting.

So, when asked about Christian Yelich’s recent opposite-field development, Don Mattingly turned the attention to a development that hasn’t yet occurred. The development he truly wants to see. Yelich has made great strides this year to prove he’s more than a slap-hitting corner outfielder. After three years, Yelich has finally shown the ability to adjust. The most important adjustment is still yet to show itself, but it might not be far away.