Are These the Best Young Hitters in Baseball History?

It is no secret that baseball is in the midst of a youth revolution. Mike Trout and Bryce Harper are, of course, two of the best players we’ve ever seen at their respective ages. They both look like they’re on the path to inner-circle Hall of Fame careers, barring health problems. They are the Willie Mays and Mickey Mantle for our generation.

But the depth of remarkable young talent around the game doesn’t stop at Trout and Harper. In another time, where those two superstars weren’t dominating the sport, the simultaneous rise of Manny Machado, Nolan Arenado, and Kris Bryant would lead to numerous stories about the sport entering a golden age of third baseman. Except third base might not even be the most loaded position right now, as the young shortstops breaking into the game now include Carlos Correa, Francisco Lindor, Xander Bogaerts, Corey Seager, and Addison Russell, with J.P. Crawford, Trea Turner, Orlando Arcia, and Dansby Swanson representing a pretty remarkable next wave; the first three of those four will likely arrive in the majors later this summer.

The future of the sport is clearly in good hands, but the most amazing thing about the present group of young players flooding the game is that they aren’t just hype and potential; they’re already some of the best players in the game. In fact, in terms of early career production, this may be the best young group of hitters the game has ever seen.

Rob Arthur wrote an excellent piece for FiveThirtyEight last summer, showing that the average age weighted by WAR has been getting significantly younger over the last 25 years. This chart from that piece illustrates the trend.

Rob’s piece focused mostly on the recent trends, but after seeing more young players dominate in April, I was curious where the current crop of young hitters rates in baseball history. To look at the long-term trends, I got Jeff Zimmerman to send me the plate appearance and WAR totals for four age-buckets for every year in baseball history: 18-25, 26-30, 31-35, and 36+. I wanted to not only look at the productivity of young players relative to their older peers, but how much playing time the young kids were being allotted.

And thanks to the graphing wizardry of Sean Dolinar, we’ve taken the percentage of total plate appearances and total position player WAR produced by 18-25 year olds and plotted it on a time-series graph to show the changes since 1900. Additionally, the graph includes the ratio of those percentages, showing the times in the game’s history when players have been more or less productive relative to the amount of playing time they’ve been allocated.

As you can see from both the PA% and WAR% lines, the game isn’t at any kind of all-time peak in terms of total production from players 25-and-younger. Back in the Dead Ball Era, half of the playing time and the WAR produced from position players came from young hitters before the game started to get a bit older in the 1920s and 1930s. Those numbers spiked back up briefly during World War II, then climbed back up over 40% during the 1960s and 1970s, when expansion led to a significant increase in available jobs, and those jobs disproportionately were filled by young hitters.

Those numbers receded back towards 30% over the last 20 years, coming back in line with the historical averages. Since 1900, the overall average shows that 18-25 year olds have received 32% of all plate appearances and accounted for 29% of all position player WAR. Teams have been willing to trade some slight underperformance from young hitters for the promise of significant improvement later in their careers, and so we see young hitters historically getting a little bit more playing time than their production warrants.

Except in 2015, that wasn’t the case at all. Last year, teams gave 33% of all plate appearances to hitters in the 18-25 bucket, a perfectly normal allocation of playing time for young hitters. However, those hitters accounted for 39% of the total WAR produced by position players last year, the highest percentage baseball has seen since 1974, a year when 18-25 year olds were given 44% of all plate appearances. And that’s why we’ve included the ratio of percentage of WAR to percentage of time allotted, because when you look at the performance relative to the number of plate appearances, 2015 was the best year ever for young hitters.

1943 was the last time young hitters approached this level of production relative to their playing time, but of course, that was right in the middle of World War II, and the demographics of the league changed dramatically as many players joined the military. In 1934 and 1935, we saw similar ratios of performance to playing time as we did in 2015, but with lower levels of playing time; 30% of all plate appearances and 35% of all WAR came from 18-25 year olds in those two years. Up until now, you could probably call that the golden age of young hitting in Major League Baseball.

But not only has 2016 not brought a significant regression to the mean, young hitters were even better in April than they were last year, putting up a 1.23 ratio of WAR% to PA%, which would easily be the highest in baseball history if sustained throughout the course of the season. The drop in both PA% and WAR% is likely a seasonal issue, as teams often hold their best young players down in the minors to begin the season; I’d imagine those numbers will climb significantly as the best prospects in the game get promoted and veterans succumb to injury during the summer.

The big change, as Arthur noted in his piece, is that young position players are just hitting better than ever before. While it used to be that the kids who got to the big leagues early did so based on their speed and defense, we now live in an age where the 25-and-under crowd can swing the sticks as well as their older peers. Young hitters currently have a 98 wRC+, which would rank second in baseball history if it held up for the entire season. But this doesn’t look like a total fluke, because 18-25 year olds also put up a 98 wRC+ in 2007, and put up a 96 wRC+ in 2009, and put up a 95 wRC+ both last year and in 2005. Excluding the first month of this season, four of the top 12 offensive seasons by wRC+ have come in the last 11 years, and if the kids keep hitting like they have in April, we’ll end 2016 with five of the top 13 offensive performances in baseball history coming in the last 12 years.

Trout and Harper are the faces of the movement, but this goes beyond just those two. This is an historically unique group of young hitters in baseball, and if April is any indication of a continuing trend from 2015, we may indeed be seeing the best group of young hitters in the history of the game.