How Do Star Hitters Age? by Jeff Zimmerman November 28, 2011 With Prince Fielder and Albert Pujols hitting the free-agent market this offseason, there have been many discussions on how the two of them will age. Lots of work has been done on how an average player ages, but Pujols and Fielder aren’t your average players. Which begs the question: How do stars age, compared to the rest of the league? One of the hardest aspects when looking at elite players’ aging curves is knowing when to consider them elite. Several hitters who are playing right now appear to be sure-fire hall-of-famers — just as long as their careers don’t do an Andruw Jones nose-dive toward uselessness. To generate a list of players who seem headed toward stardom, I selected players since 1980 who had a total of 20-plus WAR during a three-year span. Also, I took the players who generated WAR of 9.5 or more in a single season. The most important idea to remember is that these players are excellent. Some of them had single seasons that were more productive than other players’ entire careers. As a result, they had further to decline than an average player. If one of these players is down 1 WAR off their peak, they are still playing at a MVP or at an all-star level. Another point to remember is that these aging curves are set for a 600 PA season and they look at the player’s skill on the field. Players may have higher WAR in their peak seasons because they play more. As the hitter gets older and begins to break down, the playing time component of WAR begins to compound the decline. Here is the graph with four curves (average players, one great season, three good seasons and Hall-of-Famers since 1955). The y-axis is in runs and about 10 runs equal one win. All players are weighted to 600 PA (more background information on how the curves are generated): A few points from the graph: Better players peak earlier in their careers. While the general population peaks at age 27, the group of good players peak at either 25 or 26 years old. At 30, great players begin to see a pronounced decline. The one- and three-year groups peak at age 25. Here is the number of runs lost from ages 25 to 30 and from ages 30 to 35 Group: Run Lost from 25 to 30, Runs Lost from 30 to 35 One Great Season: -8 runs, -34 runs Three Good Seasons: -12 runs, -24 runs Average Player: -5 runs, -17 runs From 25 to 30, the two groups lost an average of 10 runs. During the next five years, the run decline was between a 25 to 35. This loss is much more than the average player. (To reiterate: the main reason for the above-average decline is that stars have much further to fall.) Hall-of-famers don’t usually peak — instead, they plateau. From ages 24 to 30, their production is generally constant. From then on, it drops at a high rate. There’s no doubt that if Pujols retired today, he would get into the Hall of Fame. Here is his “curve” (adjusted to 600 PA) vs. that of other HoFers: Pujols’ production seems to have peaked and dropped off a little earlier than the average hall-of-famer. I hope this information doesn’t add fire to the rumor that has been floating around. For a Fielder comparison, I used the three good seasons — which he is closest to accomplishing — and the HoF curve. It’s not as nice of a match as Pujols’ curve, but Fielder looks to be headed in one of only two ways: He’s either going to maintain his current level for a couple of more seasons — or- 2011 might have been his best season and it’s all downhill from here. When people say that great players age differently, they’re correct — to some extent. In the cases of Pujols and Fielder, that’s the caveat. And it’s an unfortunate one because teams looking to sign them long-term need to know that their best years are probably behind them.