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Joe Mauer said he noticed defenses started to play him a little differently during his second or third year in the league. He would step into the batter's box, and gradually fielders changed in his sight line at the plate.

They were covering for Mauer's propensity to hit the ball back through the box.

"I'm not exactly sure when," Mauer said. "But that shortstop would go up the middle a little bit."

The shortstop has been drifting even farther up the middle for the past 15 years.

When Mauer established himself in his early 20s as a base-hitting wunderkind, there wasn't the kind of infield shifting that has become common in 2018. Mauer's strength as a hitter — put the ball in play, hit for high average — runs counter to where baseball is now: Hit as many home runs as you can, even if you strike out a bunch and hit for low average.

To stay true to his hitting style, Mauer has to combat not just pitchers who are throwing harder than ever, but also the computers spitting out information that has made infield positioning more sophisticated.

"Right now, it's probably tougher to be a hitter than any time at any point in my career," Mauer said.

As the 35-year-old Mauer finishes his back nine, he is fortifying his case for Cooperstown, a case that includes more than 2,000 hits. It's worth asking the question — would Mauer have even more hits if not for shifting, which players in previous generations never had to navigate?

One answer: Despite the common perception, shifting hasn't affected Mauer's numbers all that much.

"You just try to be consistent with your game plan and stick with it," Mauer said. "That's how I've operated, I guess."

Looking at the numbers

You can use two different sets of data to evaluate Mauer's hitting against the shift. One is from the website FanGraphs, which has shift data in games dating to 2010. The other is from MLB's official Statcast website, Baseballsavant.com, which has data from 2015 through now.

FanGraphs defines a shift not just as having three players on one side of second base, but also situations in which two players are "positioned significantly out of their normal position." The latter shift likely is what Mauer has faced through most of his career.

"It's not always just shift — it's the overall accuracy of positioning," Twins manager Paul Molitor said. "I think as an industry we've gotten significantly better at trying to put people in the right spot given tendencies. Joe trusts himself and doesn't try to worry where they're defending. He's just going to try to put good swings on the ball consistently, which he's done."

The numbers bear that out.

Mauer didn't face shifts all that much from 2010 to '14. He put only 90 balls in play against shifts during that time frame, according to FanGraphs. The number has jumped to 347 from 2015 to '18.

But his average of balls in play didn't change much compared to standard alignments. Mauer's average is .341 on balls in play against standard alignment from 2010 to '18. That drops only to .337 against the shift.

According to Baseball Savant's data from 2015-18, which designates between "shifts" (three guys on one side of a base) and "strategic shifts" (when at least one defender is playing out of standard position), Mauer's batting average of balls in play against standard alignments is .316 and actually jumps to .341 combined against strategic and regular shifts.

By comparison, players across baseball have hit .291 on balls in play against both kinds of shifts since 2017 and .305 against standard alignments.

Strategic shifts have accounted for 16 percent of Mauer's plate appearances since 2015; full shifts account for only 3 percent.

You saw the strategic shift play out in a recent home game with the Indians. Shortstop Franciso Lindor moved close to second base but stayed on the left-field side of the bag while second baseman Erik Gonzalez moved farther into the hole on the right side. That's a typical shift against Mauer — protect the hole and protect the middle.

Attacking the defense

Mauer said when he first started to notice teams shifting with regularity, he tried to put the ball where they weren't. The amount of shifting has increased a lot in the past few years, Mauer said, and his approach to beating it has changed over time.

"Certain teams do it better than others," Mauer said. "Sometimes you try to get placing the ball instead of just having a good at-bat and hitting the ball hard somewhere going well. It's more of having a plan and trying to hit the ball hard than trying to force it to the left side or right side or what have you."

Mauer also said he tries to use the shift to his advantage when it comes to guessing what pitches may be coming. If a team is playing him a certain way, Mauer said he might know what's coming and where it will go.

"Some teams over-shift and you have an idea of what they're going to do with you but they have to execute it, too," Mauer said. "When they make mistakes, maybe not putting a pitch in a certain zone, they can be exposed a little bit."

Whether teams shift or not, Mauer has always been great at getting on base when he puts the ball in play — he has a high average of .340 in that category for his career, even as his production declined this decade.

"It just seems like he finds a way to hit two or three balls hard every day and sometimes he gets a hit, sometimes they catch them," Molitor said. "But the consistency is still there."

Mauer has been affected by various injuries throughout the second half of his career, and some fans may be upset that he didn't quite live up to the value of a eight-year, $184 million deal that expires after this season.

But the numbers show the shift hasn't been a big hindrance to Mauer's career.

Chris Hine is the writer for North Score, the Star Tribune's sports analytics beat: startribune.com/northscore. E-mail: chris.hine@startribune.com