For Paul DeJong, it’s all about calm clarity and process. The St. Louis Cardinals rookie believes in coming to the plate with a plan, but also with a clear mind. He feels that if he can stand in the batter’s box and just let things happen — simply recognize and react to pitches — the results will be there.

Three-plus months into his big-league career, the results are very much there. Since debuting with the Cardinals in late May, the 24-year-old infielder has slashed a heady .287/.321/.533. His right-handed stroke has produced 100 hits, 43 of which have gone for extra bases. His 21 home runs are tops on the team.

He reached St. Louis in short order. A fourth-round pick in 2015 out of Illinois State University — DeJong has a degree in biochemistry — he had barely over 1,000 minor-league plate appearances to his credit when he got called up. Based on his performance thus far, that was enough to prepare him to handle big-league pitching.

DeJong talked about his cerebral-yet-simple approach when the Cardinals visited Fenway Park in mid-August.

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DeJong on hitting with a clear mind: “I’ve made a lot of jumps as a hitter, going from the college level to the big leagues in two years. As much as anything, I’ve tried to slow things down as much as I can. When I get into problems is when I get sped up.

“I think [my ability to slow things down] is just the way I’m wired, and how I trust in my abilities and my preparation. I don’t feel I have to try to do anything extra to produce — I don’t have to try to be somebody I’m not. I just go out there as relaxed as I can possibly be in the situation I’m in.

“There are situations where that’s not as easy. For instance, you’re on the road and you’re the last guy up… like in Cincinnati when I first got got called up, or in Chicago when I made the last out in a tight game. The visiting crowd is going crazy, so your heart rate goes up a little bit. But those are the types of experiences that are going to help me in the future. They’ll help me be able to bust through and make a contribution while that crowd is going crazy in that high-intensity moment.

“I’m striving to have that quiet, calm clarity in every at-bat. That can be a challenge, because it’s an emotional game at times. There can be situations that make you a little more amped, a little more anxious. I’m learning to control my emotions better and be able to go up there with a clear mind and execute.

“I’m looking for a fastball to hit, early in the count — I’m aggressive — and I’m looking for a pitch in a zone. I’d like to think I can take the breaking balls and force them to give me a better pitch. It’s really just about swinging in my zone until I get to two strikes and battling from there.

“I can look fastball and still hit hanging breaking balls if the speed difference isn’t too bad. It’s about looking in a zone and not swinging at a slider that looks like a fastball and then drops off. You want to be swinging at the slider that kind of jumps up — you see it pop out of the hand and you react to it. Those are the sliders I hit early in the count and for extra bases, the ones that kind of hang up there. Not the ones that dive.

“I’ve gotten better at [recognizing pitches]. My numbers in Double-A, to start the year last year, made it clear that I was a little overmatched for a little bit. Then I started seeing more and more of those 85-mph sliders, and I adjusted. I’m going to keep adjusting, and keep recognizing those pitches earlier and better.

“You have to make adjustments, but you don’t want to change your identity. To me, an adjustment would be recognizing an inside sinker that’s going to go off the plate; it starts as a strike but ends up a ball. Being able to take that pitch would be what I’d call an adjustment. It wouldn’t be about not swinging at pitches that are in. I can hit pitches that are in. I just don’t want to be swinging at the ones that start in and end up off the plate. To me, it’s about pitch selection — pitch recognition — and execution. The result takes care of itself if you handle the process.

“I studied biochemistry and that maybe helps with my problem-solving and critical thinking — what do I need to do to get better? It’s almost like following a process, kind of like biology and chemistry was for me. More than anything, I come to the park with a clean slate every single day, knowing what I need to do. It’s a matter of just going out and doing it.”