Over the last few years, Matt Carpenter developed into one of the game’s most underrated stars by exceeding at the skill set embodied by the likes of Mark Grace and Joe Mauer over the last few decades; be extremely selective at the plate, rarely strike out, hit a ton of line drives, and create value through elite levels of walks and doubles.

From his rookie season of 2012 through the end of last season, no one in baseball took a higher percentage of pitches than Carpenter, and he ranked 14th overall in contact rate when he did offer at a pitch in the strike zone. Carpenter’s unwillingness to chase pitches out of the zone, and his ability to rarely whiff on swings in the zone, allowed him to post nearly even walk and strikeout rates in an era when pitcher dominance has become the norm. While he wasn’t a big power guy — he hit just 25 home runs during those three seasons — he made up for it by posting one of the highest line-drive rates in the game, which allowed him to rank in the top 10 in doubles, so he wasn’t just a slap-hitting singles machine like some other elite contact batters.

This year, though, Matt Carpenter is different.

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The most obvious change can be seen in looking at his home run total. As mentioned, Carpenter hit 25 in 436 games over the last three years; he’s hit 21 homers in just 133 games so far this season, and has a strong chance at doubling his career-high dinger total by years end. But to get that extra power, Carpenter has made some significant sacrifices, most notably in how often he makes contact. In 2014, Carpenter made contact on 95 percent of his swings at pitches in the strike zone, ranking ninth out of 146 qualified batters; this year, he’s at 86 percent, which ranks 113th out of 153 qualified batters.

Contact rate generally has very small year-to-year fluctuations, especially contact rate in the strike zone. At the major-league level, guys mostly are who they are when it comes to putting the bat on the ball, and it’s unusual to see a guy move so dramatically down the spectrum in such short order. In fact, Carpenter’s nine percentage-point decline in a single season would rank as the second largest drop on in-zone contact rate since we have reliable PITCHF/x data to measure such things; only Justin Upton’s 2012-2013 drop of 10 percentage points would be larger. And not coincidentally, Upton also saw the drastic decline in his contact rate correspond with a power spike (going from 17 home runs to 27 home runs), as there’s a natural trade-off between how often a hitter is willing to swing and miss and the rewards they get when they do make contact.

And perhaps we shouldn’t be too surprised that this is an exchange Carpenter has decided to make. In February, Matt Holliday told Derrick Goold of the St. Louis Post-Dispatch that he would like to see Carpenter adapt as a hitter.

"It’s great to walk and have long at-bats but he’s got the potential to hit 50 doubles. We’ve seen it,” Holliday said. “He’s got the potential to hit 15 to 20 homers. We saw that in the postseason. It’s fine that first at-bat of the game if you want to take some pitches. But I’d like to see him be a little bit more aggressive. It’s in there. He showed it. It’s in there for all of us.

"I think there’s more in there,” Holliday added. “I think there’s a combination of 27 homers like (Heyward) hit in his third year and the ton of walks he drew. I think there’s potential for 25 homers and 80 walks. I don’t think we want to ask him to walk a ton. We want to ask him to be a little more aggressive and drive the ball in the gaps and not worry about leading off. The expectation for us would be to go out there and have a good at-bat and drive the ball in the gap. We don’t need you to draw a walk or try and start a rally. We’d rather have him create the rally."

Perhaps when Holliday’s playing days are over, he should go into business as a soothsayer; at Carpenter’s current pace, he’ll finish with 24 homers and 85 walks, or almost exactly what Holliday said his teammate was capable of. He hasn’t abandoned his patient approach at the plate, but he’s reduced the extremity of that approach; his 39 percent swing rate this year is up from last year’s 33 percent mark, and while he’s still one of the most selective hitters in baseball — his swing rate ranks fourth-lowest in MLB this season — he’s not on an island by himself anymore.

Most notably, Carpenter’s changing approach can be seen on pitches at the top and inside portion of the strike zone. Below, we’ll present a pair of heat maps showing his swing rates at different parts of the strike zone, the first one from last year, the second one from this year.

Look at the portion of the zone that measures the inner-third of the plate; Carpenter has increased his swing rate by 19 percentage points down-and-in, 15 percentage points middle-in, and 29 percentage points up-and-in. Additionally, he’s increased his swing rate by 15 percentage points in the upper-middle part of the zone, and 16 percentage points in the middle-high area just out of the zone. These five boxes represent four of the lowest contact areas of the strike zone, so naturally, the fact that he’s increased his swing rate in these areas will lead to lower contact rates on in-zone swings. Carpenter is also chasing out of the zone a bit more often, but the bigger change is that he’s going after pitches in and pitches up, when previously, he hunted mostly for pitches middle-away, taking strikes if need be in order to wait for something on the outer half of the plate.

And Carpenter is finding a new ability to hit for power in these areas. Below are pitch location maps for all of Carpenter’s home runs the last two years, with 2014 first and 2015 below that.

Graphics courtesy of BaseballSavant.com.

Previously, Carpenter would yank one over the fence if you threw him a centered-fastball. This year, though, he’s hitting fastballs up in the zone, plus hanging breaking balls and two-seamers running in on the inside corner. Carpenter has never really hit the inside pitch with authority before, but likely at the encouragement of his teammates, he has learned to turn on pitches inside and is now more willing to go after high-risk/high-reward pitches up in the zone.

Going after high pitches generally means more balls in the air, and inside pitches are hit on the ground less frequently than middle and middle-away pitches as well, so unsurprisingly, Carpenter’s ground-ball rate has also dropped to 31 percent, well below his 38 percent career average. However, because balls in the air that don’t go over the fence are turned into outs at a much higher rate than grounders, Carpenter has is also posting the worst BABIP of his career, coming in at .303, down from a career .331 mark. Essentially, Carpenter has traded quantity for quality, making less contact and getting fewer hits when he does make contact in exchange for getting more impactful contact when he really turns on a mistake.

For all these changes, it’s worth noting that Carpenter is essentially no more effective at the plate than he was previously; his 126 wRC+ this season is an exact match for his career average. He’s shifted from a .300 hitter with below-average power to a .260 hitter with above-average power, but that’s different more than it’s better. It’s certainly what Holliday wanted to see from his teammate, but it’s not clear that this is actual improvement; this might just be change for change’s sake, or change for responding-to-peer-pressure sake.

But at the very least, Carpenter has shown he is malleable, and perhaps what we’re seeing now isn’t the finished product. Perhaps Carpenter will take the best parts of these changes and reduce the negative effects, combining the best of both approaches and raising his game to a new level overall. But right now, he seems to have mostly exchanged strengths and weaknesses, and as the season has gone along, he’s moved even further in this direction; he’s striking out in 26 percent of his second-half plate appearances, and he’s starting to become more of a pull-hitter than his previous use-the-whole fields approach. As the league begins to adapt to his adjustments — and he likely starts getting shifted more often, like other left-handed pull-heavy sluggers already have been — it will be interesting to see how much of this change in approach Carpenter stays with.

The extra homers are nice, but Carpenter is still mostly a leadoff hitter, and trading on-base percentage for slugging percentage from your first guy in the batting order is an odd exchange to make. If Carpenter is going to stick with this new approach, it might be time to consider moving him down a few spots in the batting order.