First, Marcus Semien worked hard, every day, with Ron Washington and various tools of the trade in order to improve his defense. He’s now an above-average defender, if you believe the stats — or at least a competent defender, if you prefer your eyes.

The newest evidence of his behind-the-scenes toil comes from his production at the plate. If you look at his overall line, a little bit more patience and power has pushed his weighted, park- and league-adjusted offense up about 10 percentage points. If you look at his overall peripherals, even, it doesn’t look like much has changed. He’s pulling a bit more, but he’s hitting about the same mix of grounders and flies.

You might just chalk it up to getting a little bigger, and picking his pitches a bit better. But if you did that, you’d miss that there’s been a rapid and drastic change to his batted-ball mix this season. It’s almost a tale of two seasons.

Take a look at his pull and opposite-field percentages over the course of this season, set against his fly- and ground-ball percentages. It’s an EKG.

It looks like Semien was pulling fly balls for power early on. And then those pulled balls turned into grounders. And then Semien made the effort to go to the opposite field more.

Turns out, that’s exactly what happened. “I realized they were shifting me a lot more,” Semien told me before a game with the Giants, “and I was hitting about .190. I saw some hits out there going the other way, but I wasn’t getting consistent with it.”

Last year, defensed shifted on Semien in 10.4% of his plate appearances. This year, that figure’s up to 15.2%. And it’s taken away much of his pop, because he’s slugging .318 into the shift this year. So he ended April with six home runs — more than he’d ever put together in a month — but also a .205 average.

But going the other way isn’t a switch you flip. It took effort. “I worked on going the other way every day,” the Athletics shortstop said. “During BP, on the field, is the best way to do it, because you can see where the ball is going.”

The best trick that Semien pulled was going to the opposite field while upping his ground-ball percentage, because the opposite-field fly ball, relative to the pull fly ball, is less effective. And the opposite-field ground ball is more effective than the pulled ground ball. Of the players who added ground balls, only six players added more opposite-field percentage between April and June.

If you look at the last part of that graph above, you’ll see that Semien is dealing right now. His opposite-field percentage is about the best it’s ever been, and he’s mixing grounders and flies near his career 1-to-1 ratio. That’s the calm part of the EKG, and it represents a ripening of his approach. All because he focused on going oppo. “It’s something that coaches want you to work on,” Semien said. “Because with that ball away, if you’re looking for it, and you can have success going the other way with it, and also on the ball in, that’s ideal.”

Of course, just because you can hit the opposite-field grounder to cover the outside part of the plate, and pull the fly ball for power, doesn’t mean you’ve turned into Barry Bonds. “You can’t always do both things, because you’re not always feeling that great,” smiled Semien.

Sure. That’s why you work hard, every day.