Yesterday, Yonder Alonso hit a home run. Used to be, that would be notable because Yonder Alonso home runs didn’t happen very often. This year, that home run was notable because it was ninth of the year, matching his career high for home runs in a season. Alonso matched his career-best home run total on May 7th, in his 29th game of the 2017 season.

You can only do something like that if you haven’t hit many home runs previously, and there are few regular corner players who have hit fewer home runs and kept their jobs than Alonso. From 2012 through 2016, when Alonso racked up over 2,200 plate appearances, he managed to launch all of 34 home runs, one fewer than Andrelton Simmons hit during that same time period. James Loney hit seven more home runs than Alonso did during that stretch, and Loney was the probably the most Alonso-like first baseman in baseball; James Loney also just got released from his minor league contract over the weekend, if you’re curious about league-wide interest in low-power first baseman on the wrong side of 30.

But low-power first baseman apparently doesn’t describe Alonso anymore, as he’s currently tied (with Bryce Harper, among others) for ninth on the 2017 home run leaderboard. His .356 ISO ranks even better, putting him fifth overall, one spot ahead of Harper. Yeah, it’s early, but Alonso is showing every characteristic of a guy who revamped his approach and might have salvaged his career.

To start, we have to mention that Alonso told Eno Sarris that he was trying this back in March.

“Did some mechanical things but also intent was important,” Alonso said in camp. “I’m trying to punish it more, get it in the air.” He agreed that aiming to put the ball in play in the air more was the major key for him this offseason as he worked.

As Travis Sawchik has noted in roughly half of the posts he’s written since joining FanGraphs, a lot of people are talking about the positive impacts of elevating the ball this year, so Alonso isn’t the only one who said he was trying to get more fly balls this spring. However, it’s always helpful when a player notes that he’s trying to do something before he actually does it, and no one has succeeded in changing their batted ball profile more than Alonso this year.

After beginning his career with a pretty normal batted ball profile, Alonso now has the seventh-highest flyball rate in MLB this year. But fly ball rate can actually be a little bit deceptive, as some hard hit air balls are classified as line drives, and those are more productive than fly balls. If you just sort the GB% list in ascending order, you’ll see Alonso is third lowest on that list, behind only Ryan Schimpf and Trevor Story, the two most extreme flyball hitters in baseball.

75% of Alonso’s batted balls this year have been hit in the air, a staggering number, and the kind of change that doesn’t just happen on accident. After six years of slapping singles around the field, Alonso is now trying to elevate the ball, but maybe more importantly, he’s trying to hit the ball hard.

Last year, Alonso’s average exit velocity on balls tracked by Statcast was 88 mph, and 92 mph when he hit it in the air, both marks appearing right around the league average. This year, he’s up to 90 mph in overall exit velocity and 94 mph when he hits it in the air, giving him a similar EV line to guys like Eric Thames. As Alonso said, he’s trying to “punish” the ball more, and to do that, he’s trading contact for a more aggressive, damage-inducing swing.

Prior to this year, Alonso’s thing was not striking out. That was his carrying skill, the one thing that kept him in the big leagues despite his lack of power or speed. This year, though, Alonso is striking out in 22% of his plate appearances, up almost eight percentage points from last year and nearly 10 points from two years ago. By swinging harder and swinging up — his average launch angle has gone from 10 degrees to 21 degrees — Alonso is basically reinventing himself as a hitter.

And while it’s both correct and necessary to be skeptical of claims that a player has become something else entirely at age-30, especially after just a good 30 game stretch, it’s worth noting that Alonso isn’t just getting lucky here.

At Baseball Savant, MLB has used the Statcast data to create an xwOBA metric, giving a player’s expected results based on his exit velocity and launch angle, plus adding in the actual results of his non-batted ball plate appearances. This gives us a decent idea of who is actually hitting the ball hard with regularity. Among players with 75+ PAs, here’s the current top 10.

You wouldn’t think “he has the same expected wOBA as Eugenio Suarez” would be a good thing, but Alonso’s .436 xwOBA is a match for his actual wOBA, suggesting that his results haven’t been inflated by good fortune. Based on historical outcomes of balls struck similarly to what Alonso has done in the first five weeks of the season, you would expect these kinds of elite slugging results.

Now, that doesn’t mean that he can keep hitting the ball like this all year. Alonso isn’t going to keep this up, just as Ryan Zimmerman isn’t going to break the all-time home run record. Small sample size can still apply to Statcast data too, so we don’t want to overreact to a month’s worth of Alonso hitting this well, even if it doesn’t look like a bunch of his fly balls have just carried over the fence.

But there are just far too many examples of guys making this kind of transformation to ignore the possibility that Alonso could keep hitting at a high level. Justin Turner was an Alonso-esque hitter until he figured out how to hit the ball hard at age-29, and while his transformation wasn’t immediate, he’s become a guy who makes extremely loud contact in the air on a regular basis. Daniel Murphy was last year’s elevate-and-celebrate poster boy, tapping into his power at age-31 after a career of slapping the ball around. And of course, J.D. Martinez and Josh Donaldson have been two of the most outspoken proponents of these kinds of changes, and both have sustained their success to a point at which they are now unquestionably among the game’s best hitters.

Because baseball is a game of adjustments, we’re going to have to see how Alonso does once the scouting report on him changes. So far this year, he’s actually seen a higher rate of pitches in the zone than he has throughout his career, and that isn’t going to last if he keeps hitting bombs left and right. At some point, pitchers are going to stop giving him pitches to hit based on the “oh, it’s just Yonder Alonso” idea, and he’ll have to show he can still produce when he’s getting pitched around.

But strike zone judgment has generally been a strength of his, and based on his history, it seems like he won’t just go hacking away at pitches out of the zone. Maybe the power won’t stick around forever, but if pitchers stop throwing him so many strikes, perhaps the walks will go up, and Alonso could still settle in as a significantly better hitter than he’s been previously. He has a lot of room to regress and still have it be an improvement over what he was.

Over the winter, I wasn’t entirely sure why the A’s were bothering to bring Alonso back. They didn’t look like contenders, and wasting 600 at-bats on a low-upside guy when they could otherwise be giving that opportunity to a younger player who might be worth something to their franchise long-term seemed like a weird use of playing time. But this is the new reality; a lot of guys we think of as low-upside are apparently quite capable of changing their ceilings if they put the work in.

And by bringing Alonso back for one more go around, the A’s might now have one of the most interesting trade chips of the summer. Or perhaps they’ll try to re-sign him to a deal that keeps him from free agency this winter, pairing him with Khris Davis to form the most unlikely middle of the order threat in baseball. Either way, Alonso looks like a pretty interesting player now, and while he’ll have to prove this isn’t just a hot start, there are plenty of reasons to think that Alonso has made the kind of changes that could stick.