
Photo by John Fisher - Getty Images
Jackson Chourio
By nearly any measure, Jackson Chourio’s 2024 MLB debut was an unquestionable success. The question now, however, is what to expect from his encore campaign.
Chourio was one of the best rookies in Brewers’ franchise history. Last season he batted .279 with a .338 on-base and .467 slugging, and those numbers are all the more impressive when factoring in the slow start he had to overcome to get there. On June 7 of last season Chourio had appeared in 54 games and was hitting .209 with a .251 on-base and .337 slugging, but from that point on he hit .306/.363/.525 with 15 home runs and 15 stolen bases.
Baseball Reference estimates that Chourio was worth 3.8 Wins Above Replacement in 2024, and that number combined with his age puts him in incredible company. Before Chourio there were only 45 players in MLB history to accumulate three or more WAR in their age 20 season. Ten of those players are either still active or recently retired, but 19 of the other 35 (54%) are in the Hall of Fame. Several of the greatest players of all time are on that list.
While Chourio may be on an all-time great career trajectory, the short-term prognosis for his development is less certain. Among the same group of 45 players mentioned above, less than 25% followed their big age 20 season with an even bigger year at age 21. About a third of them continued to perform at about the same level, and 17 of the 45 were significantly less effective than they had been the year before. Here are some precedents from each of those groups:
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Players Who Got Better
Andruw Jones had already played in 31 MLB games in his age 19 season, but his campaign as a 20-year-old in 1997 was his first foray into stardom. He played in 153 games for the Braves that season and had a .745 OPS with 18 home runs and 20 stolen bases. In part fueled by his elite defense, Baseball Reference estimates his value that season at 3.3 WAR. The next season Jones played more, hit for more power and more than doubled his value, posting a 7.4 WAR season. Jones’ Hall of Fame candidacy has been complicated by a relatively young decline and off the field issues, but he remains on the ballot and seems likely to get in eventually.
Ronald Acuna, Jr. was a player who, more like Chourio, accumulated nearly all of his value on the offensive side of the ledger during his early seasons. Acuna accumulated 3.9 Wins Above Replacement during his age 20 season in 2018, then followed that up by leading the National League in runs scored and stolen bases in 2019, a season when he hit 41 home runs and stole 37 bases. Acuna finished fifth in the voting for National League MVP that season, an award he went on to win in 2023.
Players Who Stayed the Same
Like Andruw Jones above, Adrian Beltre had already gotten some playing time in the majors during his age 19 season before emerging as one of the game’s great players as a 20-year-old. Beltre was worth nearly four wins for the 1999 Dodgers, appearing in 152 games and hitting .275 with a .352 on-base and .428 slugging while connecting for 15 home runs and stealing 18 bases. Beltre’s peak years were still a while away, however, and as a 21-year-old he produced largely similar results that B-Ref valued at 3.4 WAR. Beltre’s best years came later, highlighted by a nine-year span from 2004-12 where he averaged 5.7 WAR per season across four franchises. Despite not making the jump from star to superstar until his seventh MLB season, however, Beltre was a first ballot Hall of Famer.
Looking further back, Vada Pinson was a near-immediate success in the majors with the 1959 Reds, posting an OPS near .900 and leading the majors in doubles and runs scored in his first full MLB season. Pinson was an extremely dynamic player early in his career, accumulating nearly 31 wins above replacement by the end of his age 24 season, but his production tailed off rapidly. Across his final eleven MLB seasons Pinson was worth just 23 wins, about two per season, and his productivity was never what it was during his early peak.
Players Who Took a Step Back
Two players on the aforementioned list of age 20 standouts are significant outliers from the others because that breakout age 20 season also turned out to be the best seasons of their careers. Former A’s outfielder Claudell Washington appeared to be on the verge of stardom when he was worth nearly five wins in 1975 but, despite playing 15 more seasons in the majors, he never had another season worth more than 3.2. Much further back, first baseman Dick Hoblitzell was one of the sport’s best hitters as a 20-year-old for the 1909 Reds but never approached that level of success again.
Plenty of players who went on to extremely successful careers, however, still took steps back after age 20 breakouts. It’s possible the best-case scenario for Chourio’s career as a whole is Willie Mays, for example, but Mays followed his Rookie of the Year, 3.9 WAR 1951 season with a 1952 season where he played in just 34 games and was experiencing diminished production even before his season ended abruptly when he was drafted into the Army. Mays returned to the majors in 1954 and had one of the greatest seasons in MLB history. Mays is one of three players on the aforementioned list of 45 whose production declined in their age 21 season but who still went on to have Hall of Fame careers.
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All told, Jackson Chourio’s MLB debut season puts him in rare air in the game’s history as even the median performers among his predecessors went on to be among the greatest players of all time. While Chourio has clearly demonstrated the talent necessary to be a longtime productive big leaguer, however, history tells us that the rise to stardom doesn’t always follow a straight line.