Rookies On The Rise
Production of rookies across Major League Baseball has steadily increased in recent years, and is nearing all-time highs.
This season has been filled with fanfare around standout rookies, such as Paul Skenes, Jackson Holliday, Jackson Merrill, and Colton Cowser. This is not exactly a 2024 development either. 2023 gave us Gunnar Henderson and Corbin Carrol, while 2022 brought Adley Rutschman, Bobby Witt Jr., and Spencer Strider. Not only have these players been good rookies, but most have ranked among the best in the game. Since 2022, 8 of the top 30 position players by WAR/162 games debuted in that span.1 For pitchers, 3 of the top 8 in WAR/162 debuted in that span.2
This level of rookie production has not been seen since the World War II era, when many players put their baseball careers on pause to serve our country overseas. At that time, new players had to step in and take their place. The table below shows cumulative Wins Above Replacement (WAR) among rookie players by year dating back to 1901. I adjusted the values of WAR to account for the size of the league (i.e., number of MLB teams). Because WAR is a counting stat, total WAR will naturally be lower when there are fewer teams, as less players are in the league and hence less output is created.
Since World WAR II, and the subsequent period of integration when many Negro League players joined AL/NL teams and were de-facto “rookies”, we have seen a steady rise in production by rookies, particularly since the year 2000.
Greater Efficiency
Wins Above Replacement is a counting stat, so the more you play, the more WAR you are likely to accumulate. In other words, how do we know if rookies have actually been better in recent years, or are just playing more? To account for this, you can look at a players WAR rate. WAR per 162 games, which scales a players WAR to a full 162-game season, accomplishes this. You can also analyze plus-stats (batting) or minus-stats (pitching), which are index stats using a baseline of 100 to indicate a player's performance relative to the league average. These naturally adjust to the league environment of each year, so players can be easily compared over eras. The table below examines average rookie WAR/162 for Pitchers and Hitters, along with average rookie weighted runs created plus (wRC+) for batters and average rookie ERA- for each year dating back to 1901.
In terms of total WAR/162, 2024 ranks 7th all-time. In 2024, average rookie ERA was 5% lower (better) than the league average, good for 9th all time, while wRC+ was a touch lower at 39th all-time. There was a bit of a dip in wRC+ this past season, but overall the trend has been an upwards trajectory over the years. ERA- has also been improving among rookies, with rookies garnering lower and lower ERAs - relative to the rest of the league - over time.
Good for the Game
This is undoubtedly a positive for the game of baseball. Youth star-power brings excitement to the sport, draws interest from young fans, and assures us that the quality of the game is continuing to improve. It begs the question, who will next year’s rookie sensations be?