So I have posted part 1 and part 2 of some research I am working on over at Fangraphs, and the second part is looking at players that have their first season of 300+ plate appearances in their early 20s including guys like Eric Hosmer and Mike Moustakas. Both players made it to the bigs for long enough to collect the prerequisite PAs in 2011, Hosmer was 21 and Moustakas 22 at the time. I am a long way from done with what I want to do with these aging curves, but we can learn a little bit about both players from what I have already done.
The first part to pay attention to is upside. The graphs in my articles are based on % of maximum wRC+ and WAR for the different age cohorts. On average what we saw in the first season was around 75% of max wRC+ for 21 year olds and 80% for the 22 year olds. Based on that the best hitting seasons for Hosmer and Moustakas respectively would be somewhere around 151 and 105. It shows something most of us would believe, that Hosmer has a lot more upside, and it shows that the upper bound for Moose may not be very high. If is expected peak is basically an average hitter, then it may not be worth any more patience with him. Hosmer on the other hand shows a likelihood of getting to a pretty high peak at some point, and possibly even an elite level with the bat if he outperforms the average.
For WAR we see a very different picture. The expected max for them using the same approach would show that both players have already been above their expected value for peak WAR in 2013 for Eric Hosmer and 2012 for Mike Moustakas. If you said Moustakas is never going to be better than 2012, at this point it would not surprise me at all. Now if Hosmer has a peak season of 151 or better wRC+ in a full season he will set a much higher peak WAR than he did last year at 3.1, but there is reason to be nervous because…
We can also look at the findings here and look at probability that they never improve as significantly as the aging curve is suggesting the average does. It looks so far, and I have more to do before I am certain of this, those above and below the curve are fairly normally distributed. That is to say that only about half of the players go above the curve, for 21 year olds that would mean start at below 75% of their max and therefore have at least one season that is about 33% better than their first. So even though Hosmer’s cohort suggests he has a good shot at some pretty great peak seasons, half of his group never pulled it off. Also, as I mentioned in the article itself, about 10% of Hosmer’s group and 16 to 17% of Moose’s never put another season as good as their first together. Both Mike and Eric have already bettered their first season, but there is still some probability that we have already seen their peak.
I’m going to be spending more time on the aging curve and some other risk factors of position players, so hopefully I will have more to tell you about this in the future. For now, I am pretty close to completely giving up on Mike Moustakas because the average peak showed that his ceiling as a hitter is probably not that great even if he does ever get on track. Eric Hosmer is frustrating, but I still hold out hope that he is just going to take longer to develop than some, but that his peak will be worth it a la Alex Gordon. Hopefully as I get farther into my current work more will become clear.