The St. Louis Cardinals' infielder is having one of his worst seasons as a major leaguer. Is it luck, changes in approach, or both?

The 2017 St. Louis Cardinals have been one of the deepest teams in baseball. According to Baseball Prospectus, they have eleven players who have been worth at least 0.90 BWARP. And yet the Cardinals find themselves two games below .500, tied with the Chicago Cubs, and five-and-a-half games back of the Milwaukee Brewers in the National League Central. The Cardinals have the depth necessary to make a playoff run, but they are lacking the star power outside of Carlos Martinez.

The team has had its share of disappointments. Dexter Fowler's five-year, $82.5 million contract is looking like a mistake when considering his age and regression offensively and defensively. Stephen Piscotty and Randal Grichuk are not developing into the outfielders the Cardinals hoped them to be. Adam Wainwright's age is catching up with him. Seung Hwan Oh, who looked like one of the best closers in baseball last year, seems like he may lose his ninth-inning role any day now.

Perhaps the biggest disappointment of the 2017 season has been Matt Carpenter. Carpenter is hitting just .237 thus far; he has never hit below .271 as a big-leaguer. He is slugging just .449 after slugging .505 in each of the past two seasons. He has been worth just 1.3 wins above replacement according to Fangraphs, by far his worst pace since his rookie season.

What’s wrong with Aledmys Diaz? Photo by Dilip Vishwanat/Getty Images The 2016 breakout star hasn’t been able to produce at the same level in 2017. What’s behind his slump, and how likely is a rebound?

By no means has Carpenter been a bad hitter. He has still been 14 percent better than the average hitter, according to Fangraphs' wRC+. He has spent most of his time at first base this season, yet still has the ability to slide over to second or third base if need be. He would be an excellent addition to almost any infield in the major leagues.

But the Cardinals need Carpenter to be great, not merely good.

Carpenter's struggles can presumedly be attributed to his newfound extreme fly ball approach. His fly ball rate has risen every season since 2013, with huge spikes between the 2014 and 2015 seasons, and from last season to this season. So far in 2017, more half of Carpenter's balls in play are fly balls. His fly ball percentage of 50.7 percent is fifth-highest in the league.

This partly explains his drop in batting average. While his fly ball rate has skyrocketed, his line drive rate has fallen. His 22.6 percent line drive rate is the lowest of his career, down from 28.5 percent and 26.2 percent in 2015 and 2016, respectively. He is batting just .205 on fly balls and .653 on line drives this year.

Over the last two seasons, he is also pulling the ball a lot more than he did early in his career. His pull percentage is up above 45 percent in each of the past two seasons after never posting a pull percentage over 40 percent before 2016. This leaves Carpenter much more susceptible to the shift. Seventy-seven percent of Carpenter's balls in play have come against the shift, according to FanGraphs' shift data. For contrast, in 2015, he faced the shift for just 15 percent of his balls in play.

It'd be easy to say his fly ball and pull-happy approach can explain Carpenter's drop in production, but that is not the entire picture. He has actually been one of the most unlucky hitters in the league. His batting average on balls in play is just .256, 21st-worst in the league, after having a BABIP over .300 in every other one of his major league seasons. He has been in the bottom half in the league in batting average in ground balls, fly balls, and line drives.

His low BABIP allows one to wonder if he's simply not hitting the ball as hard as he did in the past, due to age, injury, or any number of reasons. That has not been the case. Carpenter is hitting the ball just as hard as some of the best hitters in the league. He has a higher average exit velocity than Joey Votto, Jay Bruce, and Jake Lamb. His Barrel percentage of 10.6 percent is higher than Bryce Harper and Mike Moustakas. He ranks eighth in baseball with a hard-hit percentage of 45.1 percent.

It is puzzling how a player can make better contact than almost anyone in baseball and yet still fail. Sometimes there is no other way to explain it than just luck. Although Cardinal fans are disappointed with his performance thus far, this bodes well for his second-half of the season.

Carpenter has another thing working in his favor: Not only has he completely revamped his entire batted ball approach, he has become the most patient hitter in baseball. He is swinging at just 34.5 percent of all pitches and 17.2 percent of pitches outside the zone, both the least in MLB. Unsurprisingly, he leads the major in walk rate at 17.5 percent, 0.8 percentage points ahead of second place Aaron Judge. He has always been very patient at the plate, but he has taken it to another level in 2017.

Matt Carpenter has become the embodiment of modern baseball and the fly ball revolution. He is hitting more fly balls and taking more walks than almost anyone. He has embraced the strikeout as a part of his game rather than something to avoid. Although not as many balls have flown out of the yard as Carpenter has hoped — just 14 home runs so far in 2017 — if he has even just average luck he won't have a hard time hitting just as many in the final two-and-a-half months.

When taking into account Carpenter's track record and relative youth (still just thirty-one-years-old), we can imagine him recovering in the second-half. Whether that recovery can pull the Cardinals over .500 and into the playoff race remains to be seen.

Dylan Svoboda is a writer for Beyond The Box Score and BP Milwaukee. You can follow him on Twitter at @svodylan.