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This adjustment made all the difference for Acuna

Change in batting stance has led to amazing second half for 20-year-old slugger
MLB.com @mlbbowman

ATLANTA -- Braves hitting coach Kevin Seitzer could see the tremendous physical potential, and he was well aware of the accomplishments that had earned Ronald Acuna Jr. the status of being baseball's top prospect. But Seitzer also knew that the 20-year-old phenom was destined for frequent frustration if he did not make the necessary mechanical adjustments shortly after Atlanta manager Brian Snitker reached his breaking point just before the All-Star break.

In the midst of occasionally displaying his five-tool talents, Acuna was too frequently taking off-balance swings, chasing fastballs up in the zone and simply going through the growing pains you'd expect from a kid who reached the Majors with less than 600 plate appearances above the Class A Advanced level.

ATLANTA -- Braves hitting coach Kevin Seitzer could see the tremendous physical potential, and he was well aware of the accomplishments that had earned Ronald Acuna Jr. the status of being baseball's top prospect. But Seitzer also knew that the 20-year-old phenom was destined for frequent frustration if he did not make the necessary mechanical adjustments shortly after Atlanta manager Brian Snitker reached his breaking point just before the All-Star break.

In the midst of occasionally displaying his five-tool talents, Acuna was too frequently taking off-balance swings, chasing fastballs up in the zone and simply going through the growing pains you'd expect from a kid who reached the Majors with less than 600 plate appearances above the Class A Advanced level.

"Snit said about three days before the break, 'I'm about done watching his at-bats. It's gross.'" Seitzer said. "I had been waiting for the right time to make changes to his setup. [Snit] said, 'Now is the time.'"

Those four words spoken by Snitker, combined with the instruction and application that followed, stand as one of the primary reasons the Braves are possibly just days away from clinching the National League East. Acuna has carried the team throughout the second half, and he's led some to wonder if he'll be drawing Mike Trout-level praise as early as next season.

"He's the best player I've ever seen, he's just unbelievable," Atlanta center fielder Ender Inciarte said after Acuna homered eight times within 34 at-bats spanning from Aug. 8-14.

 Video: Acuna Jr. hits 6 homers over 5 straight games

Since applying the mechanical adjustments and moving to the leadoff spot immediately after the All-Star break, Acuna has hit .320 with 19 home runs and a 1.067 OPS. Top NL MVP Award candidate Christian Yelich of the Brewers is the only player in the league with more home runs during that span. Yelich and the Dodgers' Justin Turner are the only NL players with a higher OPS.

To truly appreciate the elite level Acuna has reached, it's best to look back at the beginning of this year's journey, when he hit .249 with seven homers and a .742 OPS over 184 plate appearances before the break. He struck out in 30.4 percent of his plate appearance and drew a walk just 6.5 percent of the time.

Since the break, Acuna has struck out 21.7 percent of the time and drawn a walk in 11.6 percent of his plate appearances.

"The first day after the break, the timing with his swings was night and day," Seitzer said. "I think he went, 'Holy cow, I'm seeing the ball so much better, and I feel better and I'm on time.'

"Then, the confidence came quickly. We started seeing him chase less sliders and swing at fastballs up. When he started making them come to him in the zone, the kid is a really good hitter on secondary stuff. If you hang something on the first pitch, he's going to smoke it."

Now to rewind back to when Snitker gave the go-ahead to Seitzer, who expressed the need for a mechanical change while conducting a pre-break evaluation that focused on a number of metrics, including contact rate, exit velocity and launch angle.

"Mechanically, we put him in a different stance to try to simplify things," Seitzer said. "All I told him was, 'Get in an athletic position and get your hands back,' because he was late getting his hands back. When he'd go into his leg kick, he'd really fall forward."

Video: ATL@NYY: Sabathia fans Acuna, leaves bases loaded

When Acuna debuted at the Major League level in April, his bottom hand was angled and his bat barrel rested above his right shoulder. So when he leg kicked and began to load, his hands moved back before coming forward. The fact that Acuna has incredibly fast hands occasionally masked this flaw. But it was not enough to prevent frequent frustration.

Seitzer's solution was to get Acuna's hands further away from the body, and he instructed Acuna to adjust his bottom hand enough for the bat to be more vertical in his stance. The adjustment essentially eliminated the need for the young slugger to move his back after he leg kicked and began moving forward with his swing.

"He was ready to make the changes," Seitzer said. "This kid has done everything we've asked him to do. He's been unbelievably coachable."

Acuna believes slightly opening his stance has also proved to be quite beneficial.

"I feel like it's helped me recognize pitches a little better," Acuna said through an interpreter. "When I had more of a closed stance, I'd open up more during the stride and it would make it tougher to recognize the pitches."

Video: WSH@ATL: Acuna records 1st career 4-hit game in win

A couple numbers that truly stand out are Acuna's .388 batting average (the sixth-best average among players who have seen at least 500 pitches) and the .815 slugging percentage (trumped only by Yelich and Trout) he has produced against pitches in the strike zone in the second half. He hit .236 and slugged .425 against those pitches before the break.

"He's not missing these pitches, because he's in a much better position to fire when he wants to fire," Seitzer said. "When hitters feel like they don't have to rush to catch up, then everything slows down in terms of what you see with the recognition."

Acuna's ability to slash his strikeout rate and improve his walk rate by nearly 50 percent since the break has been influenced by the fact his first-half outside-the-zone swing percentage (14.3) has dropped to 10.2 since the break.

Looking at the in-zone swing-and-miss rate, Acuna's percentage has actually risen from 6.4 before the break to 7.6 in the second half. But his improved ability to better identify pitches and more consistently do damage earlier in the count has led to led to a lower percentage of plate appearances ending in a two-strike count -- 53 percent in the first half and 43 percent in the second half.

"He's still going to punch out," Seitzer said. "He's got power, and he doesn't get cheated when he goes. There's going to be some swing-and-miss there. But it's going to get better. He's 20 years old for crying out loud."

Mark Bowman has covered the Braves for MLB.com since 2001.

Atlanta Braves, Ronald Acuna Jr.