On April 10 at Citizens Bank Park, Brandon Marsh stepped up to the plate in the bottom of the fifth inning, looking to extend a 7-0 Phillies lead.

With runners on first and second and nobody out, Marsh took a fastball well outside from Marlins left-handed reliever Devin Smeltzer. Smeltzer’s second pitch was a sweeper just off the plate, and Marsh took it for ball two. Then he turned on a 2-0 fastball, ripping the pitch into the gap at 105.6 mph for a two-run double.

It was just one three-pitch at-bat, but it was a look at everything Marsh has improved on so far this year. Showing off a new batting stance and armed with a new approach, the Phillies center fielder has taken the next step. A month into the 2023 season, he’s been among MLB’s very best hitters.

Through Friday’s games, Marsh boasted a triple-slash line of .346/.427/.679 -- the third-best OPS of any qualified Major League hitter. He’s also been the Phillies’ best player, leading the team in FanGraphs Wins Above Replacement and tying for 19th in the Majors in that category.

"It's pretty cool, man,” Marsh said. “It's cool knowing that the work -- we get up, go grind in the offseason, even when you didn't want to half the time -- is paying off.”

For the Phillies, it couldn’t have happened at a better time.

With Bryce Harper yet to return and Trea Turner, J.T. Realmuto and Kyle Schwarber starting relatively slow, Marsh has led the way in keeping the Phillies afloat during an up-and-down April.

Here’s what Marsh has done to take his hitting to the next level -- and whether his changes are for real.

Improved plate discipline
Asked about swinging at the first pitch much less often in 2023, Marsh registered surprise.

“I’m swinging less at first pitches?” he asked. “Like the actual stat?”

Marsh might not have noticed, but the numbers don’t lie.

In 2023, his first full season with the Phillies after coming up with the Angels, he’s gone after the first pitch just 12 times in 89 plate appearances -- 13.5% of the time. In his first two seasons, Marsh swung at the first pitch at a 29.4% clip.

"I guess just really being selective where I want to go,” Marsh said. “If I don't see it where I like it, the worst it's going to be is 0-1. You don't want to be 0-1, but if you get fooled on a pitch, you want it to be early on rather than later. So I feel like I'm going to be really selective to start.”

The change is one of many Marsh has made in his plate discipline -- one of the biggest reasons for his breakout 2023 season.

Marsh is swinging and missing less -- just 23.1% of the time this season, down from a 30.5% mark before this year. He’s chasing pitches out of the zone less. He’s making more contact on pitches in the zone, too.

Marsh’s plate discipline, 2021-22 vs. 2023
Zone swing %: 64.8% vs. 61.0%
Zone contact %: 77.9% vs. 83.8%
Chase %: 30.1% vs. 24.9%
First pitch swing %: 29.4% vs. 13.5%
Whiff %: 30.5% vs. 23.1%

Only three hitters have done more damage than Marsh on pitches over the heart of the plate, an area in which he’s hitting .471 with an 1.118 slugging percentage -- the second-best slugging clip in the league.

Marsh’s selectivity is also visible in a statistic as simple as his walk rate. He drew free passes just 6.5% of the time from 2021-22; this season, he’s walking at a 12.4% clip.

Marsh said this season is as good as he has felt seeing the ball, and his numbers back it up.

“Just really the routine we've got going right now and before the game preparation, I just really like where my head's at, how I'm connecting with the hitting coaches, the whole staff really,” he said. “I just like where we're at; trusting the process."

Changes in the box
After acquiring Marsh, a former top prospect, from the Angels at the 2022 Trade Deadline, Phillies hitting coach Kevin Long noticed the issue right away: Marsh was consistently late on fastballs.

Game tape showed it, and the numbers proved it: In a season and a half with the Angels, Marsh hit just .233 (40 for 172) against four-seam fastballs with a .372 slugging percentage. (Since 2021, MLB hitters are batting .255 with a .444 slugging percentage against four-seamers.)

“In his case, the data backs up what you see, because you could see him get to his front side late, and you look at the data, and it confirms that,” Phillies manager Rob Thomson said. “So then you look for objectives to try to make him better.”

The Phillies have done that. Long’s work with Marsh has resulted in significant changes that have helped the 25-year-old outfielder get his head around more quickly on fastballs. Marsh’s stance itself is different; he has gone from standing upright at the plate to more of a crouch. The Phillies scrapped a toe-tap Marsh had used with the Angels.

Long said the changes are designed to back up Marsh’s contact point with the baseball, and so far, it’s worked to perfection. Marsh is crushing fastballs in 2023, posting a triple-slash line of .344/.382/.813 against four-seamers. That slugging percentage ranks 20th in the Majors this season.

"He’s done a really nice job of fixing his swing to the point where it’s explosive, it’s tight, it’s compact, it’s powerful,” Long said. “He’s in a better position, so it allows him a little more time to make decisions. Before he didn’t have that time. He’s not moving as much. His body is in the ideal position to hit.”

Learning lefties
Solving left-handed pitching is the next step in Marsh’s maturation into a complete hitter.

With the Angels, Marsh was in the lineup 35 of 49 times (70%) against left-handed starters, but he hit just .227 with one double and two home runs in 150 at-bats while striking out nearly 40 percent of the time.

The Phillies have been reluctant to turn Marsh free against lefties -- he’s started only eight of 15 games against southpaw starters and just three of seven this season -- but Marsh has stepped up his game against same-side pitching significantly.

Marsh is hitting .348 with a .783 slugging percentage in 25 plate appearances vs. lefties. He already has four doubles -- twice his total with the Angels -- and two homers against left-handed pitching this season.

Keep playing like that, and Marsh will see his name appear on the lineup card against left-handed starters far more often. Make no mistake: That’s by design.

“This offseason, working on lefties and that angle was definitely a big priority, just because I wanted the guys to be able to rely on me for 162, not just 120, you know?” Marsh said. “We really worked very hard on that aspect of the game."

Will it last?
As with any hot start, the same question arises: Is Marsh’s success sustainable?

Keeping up this level of play, at least, appears unlikely. Over the past 10 full seasons, only two hitters -- Aaron Judge in 2022 and Harper in 2015 -- have put up an OPS higher than Marsh’s current mark of 1.105 when all was said and done.

Marsh’s .469 batting average on balls in play (BABIP) will come down with time; the league average is .296 so far this season. Marsh, though, has always had a high BABIP, owning a career mark of .386; hitters with speed and those who hit the ball hard tend to produce higher BABIP figures.

Statistics based on average launch angle and exit velocity say Marsh has overperformed so far this season. The gap between his .465 weighted on-base average and his .349 expected wOBA is the second-biggest for any qualified hitter.

But Marsh has made undeniable progress. His xwOBA was just .287 in 2022; in his rookie season, it was .324. The reasons are evident: Marsh’s new stance in the batter’s box is paying dividends. The tweaks to his approach at the plate have made him better. He’s become a threat against left-handed pitching.

Of course, only time will tell whether those improvements are here to stay.

“It's a great feeling, but we've got a lot more ball to play,” Marsh said. “So we've just got to keep going."

Paul Casella contributed reporting to this story.