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# How Will Prince Fielder Age?

While the upcoming Free Agent crop isn’t the deepest in recent memory, there are a few sexy names at the top of the list. One of those names is of course Milwaukee Brewers first baseman Prince Fielder. Looking at his stats, we see a player who has accumulated 15.3 WAR over the last three seasons and is a perennial threat to launch 40 home runs and get on base over 40% of the time. However, due to his less than slim body type, it is not prudent to assume that he will age like most other Major League players.

In order to attempt to predict what Fielder will do over the life of his next contract, we should compare him to players with similar body types. Jeff Zimmerman has put together a list of 205 players who weigh more than 3.25 lbs per inch of height in order to construct an aging curve. To put that in perspective, a 6’0″ tall player would have to weigh a minimum of 234 lbs in order to be included in the sample.

Below is a graph that shows the aging curve of the heavy players we identified, and the curve for average sized players. Across the x-axis is age, and the y-axis runs (batting, positional, UZR), with 0 being the peak year. The y-axis shows how many runs below the peak year they are at a given age.

Two things immediately jump out from this graph:

1)   Heavy players peak a few years earlier than average players

2)   Heavy players fall off the map once they are on the wrong side of 30

The second piece of information is what is of interest to us regarding Fielder. As a 27 year-old free agent he has passed his peak years according to this curve – what we want to know is how is he going to perform over the life of his next contract.

We can play around with different numbers of years on the contract, but let’s start with 7 as that seems to be the magic number recently (Sabathia, Zito, Werth, Wells).

I have put together four tables that chart expected performance based on the two aging curves. In the top two, the chart on the left models a 27 year-old average player, while the chart on the right is a 27 year-old heavy player. Both players are considered to have true talent levels of 5.5 WAR at age 27, which was Fielder’s WAR total last season. The bottom two tables are for those of you who feel that Fielder played above his true talent level last year and in reality is a 4.5 win player. Considering his age 27 season was the second best of his career and doesn’t fit the curve very well, this is a prudent assumption. For all tables, I assumed \$5 million per win in 2012, and 5% inflation thereafter.

According to these aging curves, to treat Prince like an average player would cost a team over \$17 million on a 7-year deal. This may not seem like a huge amount relative to the Major League payroll, but I am sure every Amateur or Latin Scouting Director would love to have that amount added to their budget.

As we can see from these two charts, the major disparity in value occurs in the last two years of the contract when the heavy player regresses badly in his early 30’s. Given this information, it would be prudent to try and sign Fielder to a 5-year deal. Unfortunately, that is generally not the way the market operates, as most General Managers can’t plan to be around seven years from now, and are more concerned with production in the immediate future. There is no denying that Fielder would boost almost any teams offence over the next several seasons.

Another factor to consider is defense. Fielder’s UZR numbers are already well below average (-36.4 runs in his six full seasons), and it is entirely possible that he could be a full-time DH before he turns 30. Locking a big money player into the DH spot can severely cripple a franchises financial and roster flexibility.

One thing we should note, and is often the case when dealing with comparable players, is that you can run into sample size issues. As you can probably tell by looking at the curve, we do run into this problem at the older ages of the heavy player curve. The fact that production actually increases from age 30 to 31 is counter-intuitive, and is due to a couple of big seasons throwing off the curve. However, the fact that the size of our sample erodes to this extent shows that a significant percentage of heavy players lose enough skill that they are no longer MLB calibre players. Because Prince is good enough that he has a lot of talent to lose before he becomes a replacement level player, there is not the risk of him immediately bottoming out, but this overall deterioration of skill among heavy players is worrisome.

While the data isn’t perfect, I think it is safe to say that signing Fielder to a Mark Teixeira contract (8/180) would be an incredibly risky move, especially considering some of the worst case projections have him providing only \$122 million in value. While this figure only encompasses seven years of playing time, he will probably have decayed to the point where he would barely be above replacement level in year 8. Only time will tell if he continues to be productive into his 30’s like David Ortiz and Jim Thome, or collapses like Mo Vaughn and Adan Dunn.  Either way, it is clear that his best days are behind him. Unless I am running a team that is a serious World Series contender over the next three seasons (flags fly forever), I am extremely reluctant to hand over the contract that Fielder and his agent Scott Boras are going to want.