In 2015, A.J. Pollock posted the sixth-best WAR in baseball. The Arizona Diamondbacks center fielder put up 6.8 WAR — a total that trailed only Bryce Harper, Mike Trout, Josh Donaldson, Joey Votto, and Paul Goldschmidt. The 27-year-old hit 20 homers, stole 39 bases in 46 tries, rarely struck out, and complemented all that with good defense for a great season.

A fractured right elbow right at the start of the 2016 season robbed Pollock of a chance at a repeat, and last year he turned in a diminished version of his 2015 season while missing time due to a groin strain. Last year might have put to rest any ideas that the Pollock of old would return. The 2015 Pollock hasn’t returned this season, either. Rather, we’ve seen a new-and-improved Pollock who could be better than the burgeoning star we thought we had three years ago.

Through 33 games, Pollock already has 10 home runs, three triples, and nine doubles, his 22 extra-base hits tied with Mike Trout and behind only Mookie Betts and Ozzie Albies. Pollock’s .306/.362/.669 line produces a 173 wRC+ that ranks fifth in the sport, with his 2.1 WAR coming in behind only Trout, Betts, and Didi Gregorius. He’s on his way to a great year, and through the first 33 games of the season, he’s hit better than he ever has. The graph below shows Pollock’s 33-game rolling average of his wRC+ over his career.

It looks like, for a time in 2015, he might have been as productive as he is now, and then there’s a section in 2014 when he was even better. Prior to this year’s stretch, though his productivity was highly dependent on his BABIP. The next graph adds BABIP to wRC+.

When Pollock previously had his very good stretches at the plate, they were due in no small part to a BABIP running near .400. A really high BABIP is absent from this year’s success, as Pollock’s run has been based on power.

A cursory review of his stat line shows two major differences this year. First is the power, as Pollock’s .363 ISO is roughly double his career average. To hit for more power, hitters often sacrifice contact, which is the other noticeable part of Pollock’s stat line. His 23% strikeout rate is about 50% higher than his career mark. Pollock has been more aggressive this season than at any point in his career, both in and out of the strike zone. The increase in swings has been met with a decrease in contact, as his swinging-strike rate is up to 10% this season, well above his 7% career average. That current mark, it should be note, is still lower than league average, as Pollock still makes contact at a decent rate relative to the rest of baseball.

Let’s take a look at any potential swing changes since Pollock’s breakout 2015 season. Here’s a homer from late in that campaign.

And a homer from earlier this season.

Pollock is a little more upright, and his leg kick is noticeably higher. This is where Pollock’s leg goes at roughly the highest point, with 2018 on the left and 2015 on the right.

The positioning otherwise is pretty close, although the bat might be a bit further away from the body in 2018 and appears to be a bit higher this year as well. A bigger leg kick and load of the arms might facilitate a bigger swing and more power. T

his new change and increase in power isn’t necessarily a case of Pollock arriving late to the fly-ball revolution. Pollock was actually a pretty early adopter, and he credits Bobby Tewksbary, the coach who helped change Josh Donaldson’s swing. Pollock abandoned the old chop-down-at-the-ball approach more than five years ago on the advice of Eric Chavez, and he discussed his hitting philosophy more than two years ago in this piece by Nick Piecoro on Jake Lamb following in Pollock’s footsteps.

“I try to be as on-time as I can, but that’s not the reality in this game,” Pollock said. “The pitcher is out there trying to mess with your timing. That’s going to happen a lot. I practice all sorts, being a little bit out in front and still having the right path, the right level swing so you can still square a ball up.” Another reason a more level swing makes sense to Pollock: It helps match the plane of the pitcher, who’s standing on a mound and throwing downhill, a philosophy espoused by Ted Williams in his book “The Science of Hitting.” “Some pitchers are coming down at 10 degrees, some are coming down less at 5 degrees, but most of the time it’s coming down to you,” Pollock said. “So if it’s coming down to you and you’re swinging down, in theory that’s a really tough collision course.”

Even though Pollock changed his swing for the better quite some time ago, and had great results doing so, he still produced a good amount of ground balls and many of his hard hits were more level line drives in keeping with his philosophy above. This year, Pollock is getting a lot more air under the ball, and the change is noticeable. Below are the launch angle charts from Baseball Savant from 2015, 2017, and 2018. These charts show launch angle by frequency with the further to the right, the more often a player hits the ball at that angle.

In both 2015 and 2017, Pollock’s largest clusters were all in the 0-20 degree range, followed by a bunch of ground balls. So far this season, the biggest cluster comes above the 20 degree mark. He’s getting the ball in the air more, and it is working in the early going. Here’s what this season’s launch angle combined with exit velocity looks like.

Pollock’s average exit velocity hasn’t changed significantly over the years: he’s always generated solid velocity from his bat. This season, though, that velocity has been put to better use — namely, in the air — has started what could be a career year as Pollock heads toward free agency in the winter.

Pollock is pulling the ball more, and some of this power increase should be sustainable. He’s currently running a 26% HR/FB rate, and that’s likely to come down a bit, but unless you believe Pollock is on his way to 50 home runs, that won’t come as a surprise. With his fast start, however, 30 homers should be attainable, and he’ll have a decent shot at a 30-30 season with his speed. The Diamondbacks are off to a great start, and the newfound power of A.J. Pollock is a big reason why.