A couple days ago, Dave Appelman introduced an amazing new feature to FanGraphs: Minor League Leaderboards. This new feature will allow us track all of our favorite prospects, and learn the names of budding stars we otherwise would have missed. While the Minor League Leaderboard is an incredible tool, it is helpful, if not imperative, to take into account a player’s age and playing level. If I told you that a player had a triple-slash-line of .331/.405/.664 you might think he is a stud, but if he’s 28 and in Triple-A, it is safe to assume that the player is no prospect (there are of course exceptions).
Last season the average age of a rookie was 24.5 in Major League Baseball. This is a helpful starting point when evaluating Triple-A players. The average age of players in Triple-A last year was 28, and the vast majority of players in Triple-A are older than their Major League Rookie counterparts. While there are some 25 year olds in Triple-A that will make impacts on their respective teams, few significantly older should be considered prospects.
Below is a table of Minor League levels and their respective average ages. This is not meant to be an end-all be-all for the precise implications of age in MiLB, but rather to serve as a baseline to help give you some perspective while looking into the Minor League Leaderboard (further research will be done to look at the correlation of age and level with future Major League production).
The average age per level gives you some context for the MiLB Leaderboard, but average age is just a starting point. Statistics, framed with context, can be very informative, but without context, can be hollow. The converse however, is not the case. We can learn a lot about a prospect purely from his context. Because a player’s level is dictated by his front office, the level where he plays gives us insight into what management (which, in theory is more informed about their players than any analytic body) thinks about said player. Below is a table with the cumulative percentage of players of each age in each league:
Looking at the table above, we see that only 7% of players in Triple-A are 22 years old or younger. The bold diagonal lines, which starts from 17-year-olds in rookie ball and moves up and to the right to 22 year olds in Triple-A, outlines the path of elite prospects. The corner in the bottom right, shaded in red, shows the where players are “old” for their level.
It is my hope that the tables above will help you make more informed inferences when using the Minor League Leaderboard. In the world of analytics, context is imperative.