Back in March, Jeff wrote a post entitled “Could Aaron Altherr Be Part of the Core?” Let’s start by just lifting a few paragraphs from that piece.

Aaron Altherr has had a good spring. As should always go without saying, it’s a lot easier to have a good spring than to have a good summer. Worse players have posted better numbers, and we can seldom learn that much from these six weeks of semi-baseball. What I like here is that Altherr has put himself back on my own radar. Although he doesn’t have a clear path yet to regular playing time in Philadelphia, he could conceivably force his way. Not that long ago, he already did. Altherr’s breakout year was 2015. Then, as a 24-year-old, he trimmed his strikeouts in the upper minors, and he graduated all the way to the majors, where he posted a 125 wRC+. That’s an above-average offensive line for a debut player with quick legs and above-average defense. Altherr was going to play, and play often, until in the following spring, he busted his wrist. He missed that starting opportunity, and when he got back, he wasn’t the same. The Phillies did give him a chance. Altherr played frequently down the stretch, but his wRC+ was half what it had been. The power went away, and this is where you have to think the wrist injury took a devastating toll. Out of 309 players who batted at least 150 times in both 2015 and 2016, Altherr saw the third-largest year-to-year increase in ground-ball rate. The swing consistency wasn’t there. The swing stability wasn’t there. Wrist injuries aren’t always a valid excuse, but you can see how they could be in particular cases.

Jeff used Altherr’s big spring — he hit .303/.395/.591 in the Grapefruit League — to wonder how heavily Altherr’s miserable 2016 performance should factor into our evaluations. ZIPS and Steamer certainly weren’t very high on him, projecting an 83 wRC+ that suggested the Phillies were right to move him to a fourth outfielder role. A 26-year-old with that kind of offense is not a guy you need to make room for, even on a rebuilding team.

But ZIPS and Steamer didn’t know that Altherr might have been playing hurt last year, and as Jeff noted, his 2016 batted ball profile bears little resemblance to the one he put up in 2015 as rookie. If the wrist was a lingering problem, perhaps a healthy version of Altherr shouldn’t have such a pessimistic forecast based mostly on his total lack of power last year, especially after he showed some legitimate thump in Spring Training.

So that’s the back story. In Spring Training, Jeff found Altherr interesting, and thought maybe there was more power there than the projections thought. Fast forward five weeks, and Alther has made Jeff look like a genius.

Aaron Altherr, 2017 PA BB% K% ISO BABIP BA OBP SLG wOBA wRC+ 85 12% 25% 0.392 0.413 0.351 0.435 0.743 0.487 202

After launching a pair of home runs yesterday, Altherr now has 15 extra base hits, five more than he had all of last season. Among players with 80+ plate appearances, he ranks fifth in the majors in ISO, and his 202 wRC+ ties him with Freddie Freeman for sixth best in baseball. Or, if you want a fun comparison, here’s his slash line compared with some other guy who we’ve been writing about occasionally around here.

Alther and Thames Player BA OBP SLG wOBA wRC+ Aaron Altherr 0.351 0.435 0.743 0.487 202 Eric Thames 0.333 0.439 0.744 0.486 198

Thames has played everyday, so he has 54 more plate appearances than Altherr does, plus he has the KBO dominance, so don’t take this comparison to mean that Altherr should now be viewed as an elite hitter. But in a little under a month’s worth of playing time, Altherr has effectively matched the production of one of the biggest stories in baseball this year.

So, yeah, Aaron Altherr is interesting, and he’s currently looking a lot more like the 2015 version that made a splash in Philadelphia rather than the guy who played himself out of a job last year. As Jeff noted, his groundball rate spiked last year, but that has corrected itself in 2017, as his GB% is back to 42%, down from the 51% mark he put up last year. And his average launch angle over the last three years (11.6, then 5.6, and now 10.0) mostly confirms Jeff’s suggestion that his swing was off last year.

And speaking of swings, Altherr hasn’t gone all Yonder Alonso on his approach, but he is something of a minor “swing-change” guy. Here’s Pete Mackinin on his changes, in a piece written by David Laurila in March.

A guy who jumps out to me is Aaron Altherr. He’s adjusted his setup and his swing path. He’s gone from a long swing to a shorter swing, and he’s getting good results because of it. [Hitting coach] Matt Stairs changed him. You have to give Aaron credit, too. A lot of guys aren’t really receptive to making a change from how they’ve swung the bat their whole life. He was willing to do it, so I tip my hat to Aaron. “The key is to go directly to the ball from your launch position. Instead of A to B to C, what you’re looking for is A to C. [Altherr] has his bat on his shoulder now. He had been starting with his hands up high, and it looked uncomfortable. I always felt his swing looked a little too long. He made the correction.

Jeff noticed the hand position change in his post, so there is some mechanical explanation for Altherr hitting the crap out of the ball this year after slapping it around last year. And while anyone running a 202 wRC+ has almost certainly gotten at least a little lucky, Altherr is definitely making better contact than he did last year; his average exit velocity is up from 88 to 91 mph, and more importantly, from 93 to 98 mph on balls in the air. His airball exit velocity puts him in the same area as Ryan Braun, Manny Machado, Cody Bellinger, Yasmany Tomas, Justin Upton, and Matt Holliday.

So, while he’s not a true talent .392 ISO guy, it seems pretty likely that there’s legitimate power here. And as Jeff noted back in March, if he has legitimate power, then he’s a good player, because everything else is already in place. Altherr already showed a decent idea of the strike zone, but he’s also running a career low 22% O-Swing% this year, and his overall swing rates show a relatively patient hitter who isn’t afraid to work counts. His contact rates have hovered around 75%, a little bit below league average, but his in-zone contact rates have been either around or above league average, and this year, is up at 87%.

His swing-and-miss problem is almost entirely related to chasing pitches out of the zone, which is something that he’s doing less this year than he has previously. If you have to have a contact problem, it’s much better to have low contact rates on pitches that you can choose to take than on pitches you have to swing at. Altherr isn’t Joey Gallo or Byron Buxton, where he’s swinging through pitches in the zone, and that he can hit for real power while making above average contact on pitches in the zone is certainly encouraging.

So we have a hitter who will draw some walks, makes enough contact, and has some power. That’s a nice offensive base to build from, and he’s not exactly slow either. Toss in that he looks like he could have some real defensive value in left field, with the ability to cover center occasionally if need be, and the package starts to look pretty similar to the skillset that made Mitch Haniger a popular guy on FanGraphs over the winter.

Like Haniger, Altherr is a little older, and as a guy who might profile as a good-not-great hitter in a corner outfield spot, he probably won’t become an accepted star. But an above-average hitter who can also play defense is a very nice piece, and there’s George Springer upside to this skillset. Springer, of course, has been producing in the big leagues for four years now, and Altherr isn’t even on three good months as a Major Leaguer yet, so there’s a lot of risk here. As the league adjusts, he might not adjust back, and he very well may join a very long list of guys who were good for 100 at-bats and then got exposed.

But as a good athlete who shows some control of the strike zone, all Altherr really needed was enough power to scare pitchers into not pounding the zone in order to be a big league regular. It’s not easy to fake the kind of power Altherr is showing right now, and while there’s inevitable regression coming, he looks like he might have enough power to let everything else play.

While the Phillies pitching staff got most of the hype last year, their organization has done a pretty nifty job of turning a cast of fringe prospects into the start of a pretty interesting core group of hitters. Between Cesar Hernandez, Odubel Herrera, and now Altherr, the team could now have three solid young players who add value on both sides of the ball. There’s still holes to be filled, but right now, Altherr looks like he’s taking one of the corner outfield jobs and running away with it.