Major League Baseball Advanced Media has entered the final stages of rolling out Statcast, the system that will soon start tracking every on-field movement players make. The numbers that Statcast produces will allow us to put players under more powerful microscopes, clearing the cobwebs from the corners of our knowledge about baseball. No matter what they have to teach us, though, Statcast’s cameras and radar can’t penetrate players’ brains. For the foreseeable future, athletes’ thoughts and motivations will remain a black box.

And motivations matter. Take Twins infielder/outfielder Eduardo Nunez. Less than five years ago, Nunez’s name had enough cachet to alter the outcome of a season. When the Mariners auctioned off ace Cliff Lee at the 2010 trade deadline, Yankees GM Brian Cashman was willing to offer his team’s then–top prospect, Jesus Montero. He was willing to pay the money remaining on Lee’s contract. And he was willing to throw in Double-A infielder David Adams. But Adams had injured his ankle, so Mariners GM Jack Zduriencik asked for a substitute: Ivan Nova or Nunez, who was then Nova’s Triple-A teammate. Nunez, Cashman decided, was too good to give up. Lee went to the Rangers instead, and a few months later, he threw eight shutout innings at Yankee Stadium in Game 3 of the ALCS, a series that Texas took in six. The AL pennant and even the World Series itself may have hinged on the perceived difference between Adams and Nunez.

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Click here for more MLB Preview! Two years later, Cashman — who had once called Nunez a “future starting shortstop” — publicly lowered expectations. “I’ve had a lot of people say, you’ve got to get 500 at-bats for this guy, find a position for him as if he’s some sort of offensive juggernaut,” Cashman said. The truth, he revealed, was that Nunez was “not a great offensive player,” hamstrung by a bat that “does not profile” anywhere except up the middle. A year after that, the Yankees designated Nunez for assignment. “Enough on Eduardo,” Cashman said, with words as well as actions. This spring, Nunez — now a five-year veteran under Twins control — is fighting for his major league life, with his grasp on an Opening Day roster spot tightening and loosening in response to other players’ slumps and hot streaks. Nunez is still just 27 years old, an age traditionally associated with baseball breakouts. But it’s also an age associated with tragic demises, and if Nunez doesn’t change something soon, his career will suffer one.

How did Nunez go from being Derek Jeter’s heir apparent to fighting for a part-time role on a likely last-place team, while still in his physical prime? On the surface, Nunez’s story might sound like those of countless other disappointing players. Nunez, however, has picked up a habit that no one else has. He’s hooked on homers-in-silos, addicted to easy outs, going through life with a bad batted ball on his back. Nunez will make more than $1 million playing professional baseball this season. And unbeknownst to the people paying him, he’ll begin every game with the same goal he’s had for the past several seasons: Try to hit a popup in every trip to the plate.

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Nunez never would have started down the dark path had Jeter not hurt his calf in June 2011. A conspiracy theorist could claim that Jeter, intent on playing shortstop into his forties, had timed his injury to sabotage his likely successor. Like most conspiracy theories, though, that one seems far-fetched: Just because there’s a Major League Baseball player who’s hitting popups on purpose doesn’t mean there’s another player pulling the strings. Jeter argued against going on the DL: If he’d gotten his way, it would have been him, not Nunez, in the starting lineup on July 1, 2011, in the game against the Mets that changed the course of Nunez’s career.

No, Nunez has acted alone. But what could make a player act against his interests and play right into the opposing pitcher’s hands? To understand what happened to Nunez that night, you have to know a little bit about popups. On batted balls that MLBAM classified as popups in 2014, batters hit .021/.021/.026, according to the database at Baseball Prospectus. Baseball Info Solutions classifies popups that are fielded by infielders or travel fewer than 160 feet as “infield fly balls.” Last year, only 1.45 percent of infield fly balls resulted in the batter reaching base. Save for reaching first on an uncaught third strike — something that happened on only .28 percent of strikeouts last season — getting on via the popup is the most improbable way for a batter to be rewarded. And unlike a third strike that bounces to the backstop, a popup that falls between fielders helps a hitter’s slash stats the same as a solid line drive up the middle. It’s an exhilarating reprieve and a life-affirming reversal of fortune, like pulling the trigger in Russian roulette and having a kitten come out. A player might get attached to that feeling. A player might do whatever it took to experience it again.

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Filling in for Jeter against Mets starter Jon Niese, Nunez led off the top of the second with a bunt single. In the fourth, he doubled on a weak grounder that skipped just inside the first-base line. In the eighth, he singled on a 98 mph fastball from Bobby Parnell that came in four feet off the ground. Last season, swings at pitches that high and hard resulted in singles only 2 percent of the time; between the perfectly placed bunt, the grounder that barely stayed fair, and the unlikely single, Nunez was leading a charmed life. But his greatest luck had come in the sixth, when he’d popped up to shallow left and watched the weak ball, laser-sighted between three converging fielders, drop just out of Jose Reyes’s reach.

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After his first four-hit game, Nunez took the podium for his first press conference. “Swinging at good pitches, that’s more important [than the hits],” Nunez said. “Something happens, good.” Of course, he hadn’t swung solely at good pitches — the pitch that led to the popup was on the high side, and the pitch from Parnell was well out of the zone — but the bad pitches had produced good results, and Nunez stuck with what had worked.

The image below, generated via the FanGraphs spray chart tool, shows the location of every popup Nunez has hit in the majors, according to MLBAM’s classifications. Red circles represent outs. There’s one circle, you’ll notice, that’s not red.

That gray circle, the fateful single from July 1, seems innocent enough. But ever since it appeared, it’s been spawning red, corrupted copies of itself, like a cancerous cell. Nunez had always known that once in a while, popups paid off: The diagram below, for instance, shows every infield fly (by Inside Edge’s reckoning) that fell for a hit last season.

But it’s one thing to see someone else survive a popup, and another thing to experience it oneself. Over the rest of the season, Nunez swung at pitches more than an inch higher, on average, than he had before July 1. In particular, he upped his swing rate on particularly high pitches — those from which popups tend to be born, as this Baseball Savant diagram of infield-fly pitch locations shows.

Nunez isn’t an indiscriminate swinger at high pitches, but when he sees a truly high one, he’s much more likely to swing than the average hitter.

2010-14 Sample Avg. Pitch Height Avg. Swing Height Swing Rate, Pitches >3.8 ft Nunez 2.33 2.40 24.3% MLB 2.31 2.37 14.9%

For the new Nunez, then, every elevated pitch was a potential popup, and even head level wasn’t too high.

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And if one infield fly didn’t fall …

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… well, maybe the next one would. And if that one didn’t, it might make Nunez mad. One Nunez death stare after a foul out last season drove Lyle Overbay into retirement.

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Nunez’s tendencies haven’t totally escaped the Internet’s notice. “He has too much of an uppercut in his swing and gets under the ball too much,” Pinstripe Alley’s Mark Duggan wrote, a year after the 4-for-4 game. What Duggan didn’t realize is that Nunez’s swing was working as designed.

I’m going to show you two graphs Nunez wouldn’t want you to see — the smoking guns he’s gone to great lengths to bury. Baseball Prospectus’s MLBAM-based batted-ball classifications from Retrosheet go back to 2003; the GIF below shows the ratio of popups to fly balls for all players (with a minimum of 1,000 plate appearances) whose careers have started since then.

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Players who qualified for the list have averaged .27 popups per fly ball. Nunez, however, has hit .70 popups per fly ball. In other words, when he hits a ball in the air, it’s almost as likely to be classified a popup as it is to be classified as a regular fly ball. The next-highest qualifier comes in at a comparatively modest .53.

The second GIF, based on BIS classifications from FanGraphs, shows the career infield fly ball rate — infield flies divided by all flies — for all active players with at least 1,000 plate appearances.

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Generally, the more fly balls a batter hits, the more infield flies he hits as a percentage of those flies. Nunez isn’t an extreme fly ball hitter: His career 34 percent fly ball rate is roughly league average. However, the percentage of his flies that are classified as infield flies is more than double the usual rate, easily leading all active qualifiers. And it doesn’t take long for players’ popup rates to reflect their true talent.

One might wonder why Nunez’s single-minded quest for a second popup single hasn’t led to even more infield flies. The answer is that hitting in the big leagues is hard, even when one is attempting to do something detrimental. In situations that call for players to hit sac flies or slap the ball to the right side, they succeed in doing so only slightly more often than they normally would. Similarly, Nunez can’t hit popups whenever he wants to. The best he can do is aim high and increase his odds by putting more pitches in play. Last season, Nunez swung more often than ever before and was rewarded with the league’s lowest walk rate.

However, he has to be subtle. Turn too many pitches into popups, and eventually a coach could catch on. Whether the coach suspected his underlying desire or merely mistook him for someone who was genuinely bad at baseball, a significant statistical decline would mean less playing time, and less playing time would mean fewer popups. Fortunately, Nunez has found a way to fly under the radar: Create a diversion.

To the extent that Nunez is known for anything other than PopupGate, it’s for having his helmet fall off when he runs the bases. It’s the ultimate misdirection. Nunez has his whole team so fixated on what he’s doing with his helmet that no one has noticed what he’s doing with his bat — namely, using it to risk near-certain outs in in hopes of riding a rush he’s felt once before. From Fox Sports North, last September:

When Nunez is asked about the helmet, he just laughs. It’s a problem he had during his four seasons with the New York Yankees, and it’s followed him to Minnesota. It wasn’t an issue in the minor leagues, he said, perhaps due to what he said were heavier helmets.

Were the helmets really heavier? Or was it that just that minor league Nunez had nothing to hide? The Twins have tried adding extra padding inside Nunez’s helmet, to no avail. “It still fell off,” Nunez said, twirling an imaginary mustache. “I don’t know what’s going on.”

Good laughs today as @EduardoNunez15 gets fitted for his helmet. He said he still might need a chin strap. pic.twitter.com/scQJXzX7zI — Dustin Morse (@Twins_morsecode) February 25, 2015

“We’re all like, ‘Here it goes! Here it goes!’” Brian Dozier said, describing the gullible dugout’s anticipation. “We’re waiting for it.” And while everyone is waiting to see whether his helmet comes off, Nunez is pulling off a heist of his team’s most precious commodity: outs.

Nunez is most clever when he uses common customs as cover. Notice how he appropriates the practice of pointing directly upward after hitting home runs. The catcher and umpire think he’s sending a performance-enhancing prayer to the big batting coach in the sky. Really, though, he’s reminding himself where to aim next time.

Occasionally, Nunez gets careless and lets his disguise slip. For all of his dedication to the helmet maneuver, he has a hard time hiding his apathy about any plate appearance that doesn’t end in an infield fly. Here, in quick succession, are his reactions to a run-scoring single, a run-scoring double, and a run-scoring triple. In each instance, his body language sends the same demoralized message: Another popup opportunity squandered.

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There are signs that Nunez is spiraling — that his pursuit of the perfect popup is bleeding over into other areas of his game. It’s not enough, now, for Nunez to hit popups himself. He’s also determined to prevent opposing popups from falling, as though there are only so many popup singles per season to go around. Sometimes that popup hypersensitivity serves him well. But when Nunez has his eye on a falling pop fly, he loses all awareness of his surroundings, becoming a danger to himself and to everyone else on the field.

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Even when Nunez avoids a collision, those brief glimpses behind the mask that normally hides his true intentions have consequences for clubhouse chemistry. Tensions run high when Nunez’s popup tunnel vision takes him into another teammate’s territory.

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Naturally, Nunez has a plan for ensuring that his infield-fly infatuation on defense doesn’t tip anyone off to his agenda at the plate. What works with a helmet, he’s hoping, will also work with a hat.

Eduardo Nunez – famous for his helmet flying off at every opportunity – just had his hat fly off while chasing a popup. #Yankees — Paul Severino (@SeverinoMLB) August 15, 2013

Nunez has been one of the five least valuable players who’s made as many plate appearances as he has over the past five years. But now that we know his secret, a minus-1.9 career WAR doesn’t seem so bad. How well would Nunez have hit if he’d been trying to collect base hits the usual way, instead of by the most difficult method imaginable? Maybe he is an offensive juggernaut, with his bat voluntarily tied behind his back.

This is a story about Nunez, but it’s not only about Nunez. It’s also about how much remains hidden, even as the amount of information available about baseball increases exponentially. For the past few years, a constantly scrutinized major leaguer has made hitting popups his priority, and no one has noticed his counterproductive approach until now. If Nunez could fool front offices, field staffs, and fans for this long, we have to wonder what else we’re missing.

Thanks to Rob Arthur, Kenny Kendrena, Rob McQuown, Scott Spratt, and Daren Willman for research assistance.