Last week I wrote a post showing that there has been a sharp reduction in star players who have passed their 35th birthday. There was a lot of discussion about this on Twitter and elsewhere, mainly focusing on the likely explanations for my data. Most people seemed to believe the largest cause for this trend is “PED testing.” This might be correct, but I was trying to leave the speculation out of it and try to focus on what the data says.
A few people suggested that I should present the data for WAR/PA, rather than just total WAR for each age. I use WAR in studies like this (I have done many such studies showing contributions broken down by race) because I don’t want the replacement-level players to swamp the data. Which they would.
In the 1988-2017 period (30 years), there were 35,913 player-seasons. Here is a plot showing the annual average age, giving all players equal weight.
The same rise and fall shows up here as I showed last week. With over 1200 players every season, a drop in average age of 0.8 years in the past 12 seasons is fairly dramatic.
Of this huge pool of seasons, 70% of them are fewer than 1.0 WAR, which are (roughly speaking) replacement level. In fact, if you combine these 25,012 seasons together, they sum to less than 0.0 WAR (there is more negative value in this cohort than there is positive value).
To this end, I will “bin” the rest of the data.
Replacement (less than 1.0 WAR): 25,102 total seasons, 69.6%.
Useful (1.0 <= WAR < 3.0): 7210 seasons, 20.1 %
Good (3.0 <= WAR < 7.0): 3401 seasons, 9.5%
Great (7.0 <= WAR): 290 seasons, 0.8%
These bin choices are mostly arbitrary—Tom Tango specifically asked on Twitter whether there are fewer “old” players between 1 and 3 WAR, so I thought I might as well created a few other bins.
Now I will just show the average age of the players in each of these bins.
For the best cohort (shown in blue) I combined the “good” and “great” seasons, meaning that the line shows all seasons of at least 3.0 WAR. I do this because there are relatively few great seasons, and the “great” line becomes somewhat meaningless.
Although all four cohorts show the same rough trend, the replacement players tend to be younger (at least until recently), and the average age of the good and great cohorts both drop fairly dramatically between 2005 and 2009.
When added to the post from last week, it seems clear that the contributions of older players has shrunk dramatically in the past decade, and this is true across all levels of quality.
Finally, there was some speculation that the data I showed was partly due to teams deliberately playing younger players (to save money). Its strikes me that the players most likely to be affected by salary-based attrition would be the replacement level players, but this is the part of the roster that has aged the least. With the important caveat that teams do not know — in advance — how good their players are going to perform, it does not seem as if they are deliberately employing young players any more than they should.