Last season, we saw the emergence of then 20-year old Mike Trout outshine the similar rise of 19-year old Bryce Harper to the big leagues. Trout finished the season with the highest WAR ever by a 20-year old, while Harper finished with the highest WAR ever by a 19-year old. The occurrence of young hitters performing so well is not common, seen only in the early seasons of the likes of Alex Rodriguez, Ken Griffey Jr., and Mickey Mantle.
But here we are, 70-plus games into the 2013 season, and what we saw last year might be repeated. Twenty-year-old Manny Machado is having a very Trout-like season for the Orioles, with a .322/.354/.489 line, and on pace to hit 73 doubles, which would set a major league record. And, just like Trout last year, Machado is not only playing the field better than any other player at his position, he is also is leading all players in fielding WAR. This phenomenal performance has already generated Trout vs. Harper vs. Machado debates on many sports websites. (Don’t worry; this article isn’t one of them.)
Another similarity between Machado and Trout is that, just like what Trout did to Harper, Machado’s success has overshadowed that of another great season from a very young player. Jean Segura, at age 23, has so far posted a .330/.364/.526 line, to go along with 10 home runs and 19 stolen bases.
These incredibly young hitters performing so surprisingly well sparked the question: Are younger players performing better at the plate in recent years than they have in previous baseball history?
Since the Expansion Era began in 1961, there has been some serious fluctuation in how many wins young players have accounted for. In 2009, Mitchel Lichtman, on The Hardball Times, created a standard aging curve for batters based on linear weights. His model shows that, on average, a decline in performance begins in a player’s 29-year-old season. Therefore, only players aged 28 and younger can be considered in this question. Also, I want to look at only players who played a meaningful role for their team, to avoid being dragged down by the slew of replacement level players trotted out for a season or two by big league clubs over the years. So, our population will be limited to players under the age of 29 who compiled at least one win above replacement in any given season since 1961.
The easiest way that I could think of to show how the success of younger players has changed over time is dividing he last 50 or so years by decades (’60s, ’70s, ’80s, etc.) In the 1960s, 64-percent of players in the big leagues were 28 years old or younger. On a graph including all players who earned at least one win above replacement with age on one axis and WAR on the other, the slope of the line of best-fit is just under .7, with the correlation at a measly 0.08.
These numbers remain almost exactly the same in the 1970s, but they begin to change in the ’80s. The slope of the line of best-fit drops to 0.5, and the correlation drops to 0.06. This means that age is having less effect on WAR than it did in the past. However, in the 1980s only 55 percent of players were under the age of 29. This shows that rather than younger players performing better, age was simply having less effect on performance.
This trend continued, and drastically sped up in the 1990s, when only 48 percent of players were under the age of 29. The slope of the line of best-fit for this decade was 0.005, and the correlation between age and WAR dropped to 0.0051. In other words, during that decade, a player’s age had practically no effect on that player’s WAR.
These numbers have rebounded in the subsequent years, with the slope being about 0.2 in the 2000’s with a correlation of .03, and a slope of 0.35 so far in the 2010’s, with a correlation of 0.4. Furthermore, the percent of players in the big leagues under the age of 29 has grown to 52 percent.
One obvious possible explanation for this strange trend from the late ’80s to the mid 2000s is the prevalence of steroids in baseball. Steroids drastically altered the aging curve of major league hitters, allowing players like Barry Bonds to continue their primes into their mid or even late 30s. This could have created a lower demand for new, younger replacements for aging veterans, as well as changed the relationship between age and productivity. Assuming that the incidence of steroid use has decreased in recent years, the timeline fits well with this trend.
Another possible explanation for why young player prevalence and productivity has increased in the past few years is the increasing “savviness” of front offices. In the aftermath of Moneyball and the sports information boom, teams are recognizing that, just like in any industry, it can be more cost efficient to replace an older employee with a younger one who makes far less money. Teams such as the Red Sox have flat-out refused to sign players over the age of 30 to long term deals (except when they didn’t). They may be aware that 36-year old players are making an average of $8 million this season while 23-year-olds are making an average of $700,000.
Either way, the occurrence of very talented, very young players landing full time jobs in the big leagues is increasing, and I don’t see any reason why it wouldn’t continue to do so.