Ronald Acuna Is Quietly Getting Better And Thats Scary

PlayerYearAgeOPS+PlayerYearAgeWAR/G Ronald Acuña Jr.’s rookie year was historicFor MLB hitters age 20 or younger in a season since 1901, greatest adjusted on-base plus slugging and wins above replacement per game 20Vada Pinson195920129Mel Ott192819.032 Min. 450 plate appearances for OPS+ leaders and 100 games for WAR/G leadersSources: Baseball-Reference.com, FanGraphs 17Bryce Harper201320133Ken Griffey Jr.199020.033 2Ty Cobb190720167Alex Rodriguez199620.064 3Mel Ott192920165Mel Ott192920.051 10Ronald Acuña Jr.201820145Jason Heyward201020.039 18Tony Conigliaro196520133Bryce Harper201320.033 11Juan Soto201819143Vada Pinson195920.038 4Al Kaline195520162Al Kaline195520.051 8Rogers Hornsby191620151Frank Robinson195620.041 15Ken Griffey Jr.199020136Bryce Harper201219.034 13Dick Hoblitzell190920143Rogers Hornsby191620.037 16Sherry Magee190520134Sherry Magee190520.034 At a glance, Acuña’s early 2019 numbers actually represent a slight downgrade from that stellar rookie campaign. His OPS+ has dipped from 145 to 134, thanks to a big decline in slugging percentage (.552 to .487). Relatedly, Acuña is hitting home runs less frequently, and his isolated power is down nearly 70 points. It looks sure like a mild sophomore slump — albeit one we should all be so lucky to have.Under the surface, however, Acuña has made some impressive strides this year in two important areas: plate discipline and defense.Acuña’s 2018 walk rate of 9.2 percent was already better than league average — particularly impressive considering the whole “20-year-old rookie” factor — but his 2019 rate is up to 12.7 percent, which ranks 35th in baseball. He’s seeing more pitches (4.61 per plate appearance, second-most in baseball) and consistently getting into good hitter’s counts more often than he did a year ago. At the same time, Acuña has been whiffing a lot less so far in 2019. He struck out in 25.3 percent of his plate appearances last season, which ranked him around the bottom quarter of MLB hitters, but this year that rate is down to 21.8 percent, comfortably in the top half of the league.Those changes give Acuña an overall strikeout-to-walk ratio of 1.72, which is the second-lowest in baseball for a hitter his age. Since a player’s batting eye is a core leading indicator for his underlying hitting skills, Acuña’s improved strike-zone judgment is a great sign of his ongoing development at the plate.The other area in which Acuña has improved is defense. We combined the Ultimate Zone Rating figures found at FanGraphs and the Defensive Runs Saved numbers at Baseball-Reference.com and found that Acuña was no better than an average outfielder last season. (And he might have been worse than that — another prominent metric, Michael Humphreys’ Defensive Regression Analysis, considered him to be 3 runs below average.) This season, Acuña’s numbers are up no matter which source you consult; he’s on pace to have improved by about 10 runs — or 1 entire win — if he ends up playing the same number of innings as in 2018.4Which probably undersells his potential improvement, because Acuña was limited to 111 games last year between injuries and Atlanta’s service-time chicanery.The advanced fielding stats may just be catching up with what the eye test already knew about Acuña’s defensive potential. FanGraphs’ annual poll of fan fielding assessments had already judged Acuña to be one of the most talented left fielders in the game last season, thanks to his tremendous first step and speed to the ball off the bat. But now that he’s putting those skills to use in the metrics, Acuña’s potential value looks even greater: Per 162 team games, he’s tracking for 7.0 WAR this season, which basically matches what Ken Griffey Jr. and Albert Pujols had at the same age.Acuña’s dip in power this year is a bit puzzling, particularly since his Statcast hitting metrics — including exit velocity, hard-hit ball rate and “barrels” (balls hit with the ideal velocity and launch angle) — are also down across the board. Some of that might come down to the injury that kept him out of Sunday’s game: “It’s been on and off,” Acuña told reporters through an interpreter after picking up four hits but exiting Saturday’s game early. “I’ve felt it for a while, so it wasn’t today. Today, it just kind of grabbed at me after I had a quick swing like that and got out of the box pretty quickly. That’s when I felt it. But I felt good coming into today, as always.”But assuming his back isn’t an ongoing issue, Acuña should get plenty more pitches to crush as the season goes on, given his improved willingness to wait out favorable counts. Acuña may not be launching balls out of the park left and right like Bellinger at the moment — he hasn’t homered since April 16, in fact — but the foundation of his game still has superstardom stamped into it as much as ever. 5Mickey Mantle195220162Ted Williams193920.046 14Mel Ott192819139Ronald Acuña Jr.201820.035 When the Los Angeles Dodgers take on the Atlanta Braves for a three-game series starting tonight, all eyes will be on a precocious young star who’s taken his game to the next level early this season. We are, of course, talking about L.A.’s Cody Bellinger … right? Certainly Bellinger has been great so far, and he was just named the National League’s player of the month for April. But “precocious young star” could also fit Bellinger’s counterpart on the Braves: Ronald Acuña Jr. Acuña’s ongoing development as a superstar hasn’t gotten as much attention as Bellinger’s, particularly during his recent slump and injury absence over the weekend, but Atlanta’s 21-year-old left fielder is showing important signs of improvement, too, despite surface-level numbers that can’t match those of his Dodger rival.Acuña’s 2018 rookie season already put him in the history books. After being held down in Triple-A until April 25, he posted the 10th-best adjusted on-base plus slugging (OPS+) of any player age 20 or younger in a season since 1901,1Minimum 450 plate appearances. edging out fellow NL East outfielder Juan Soto in the process, and he had the 14th-most wins above replacement2Averaging together the WAR versions found at Baseball-Reference.com and FanGraphs. per game3Minimum 100 games. of any 20-or-under hitter over the same span, besting Bryce Harper, Ken Griffey Jr. and Willie Mays. Adj. on-base plus sluggingWins above replacement per game 6Alex Rodriguez199620161Mickey Mantle195220.046 1Mike Trout201220168Mike Trout201220.074 19Jason Heyward201020131Willie Mays195120.032 7Ted Williams193920160Ty Cobb190720.046 9Jimmie Foxx192820148Jimmie Foxx192820.040 12Frank Robinson195620143Manny Machado201320.037

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