When will Pablo Sandoval move off third base?

Pablo Sandoval is undoubtedly due for a big payday. At age 28, the free agent third baseman is a middle-of-the-order bat and an above-average fielder at a premium position. He is reportedly seeking a six-year deal; how will his production decline as he ages from 28 to 34? Though young for a free agent, Sandoval’s weight makes his forecast more complicated. Some great work has been done in the past on how heavy players’ offensive production ages, but what about his defense? Sandoval’s combination of above average defense and above average weight makes him an interesting case.

In terms of his weight Sandoval is a trailblazer at the hot corner. Deep into the history of the past 143 years of recorded baseball history no player of Sandoval’s proportions has played more than a season’s worth of games at third base. One big reason to believe Sandoval will not be able to stay at third base is simply no one of his size has done it before. Here are the top ten biggest third basemen in history in terms of pounds per inch.

We can see that Sandoval is somewhat in his own category here. Uribe is in the same weight class and useful to look at as a model of a bigger player making it well into his thirties while staying at third. Despite the similarities, there seems to be a line to be drawn between the 3.3ers and the 3.2ers. That extra tenth of a pound is not insignificant -- it equates to roughly an extra seven pounds for a six-foot player. Guys appearing on this list such as Rolen, Tejada, and Hinkse were never really dogged for their weight and were always seen as thick, but never overweight.

The most important takeaway here is that we won’t be able to make a weight-specific aging curve for third basemen. There simply aren’t enough comparable observations for it to be a useful exercise.

Accepting the fact that we will have to leave weight out of the picture here, I decided to instead turn my focus to the defensive spectrum. This was one of the first Bill James sabermetric concepts I remember internalizing. It is the simple idea that there exists a spectrum of positions, with the easy on one end and the more difficult on the other. As players get older, they tend to move along the spectrum from difficult to easy, and rarely go backwards. While it is not set it stone, the spectrum usually takes this form:

SS>2B>CF>3B>RF>LF>1B>DH

Catchers are left omitted, since they are often considered a special case. As I’ve written it, players tend to move left to right as they get older. With this concept in mind, I decided to make an aging curve examining the ratio of games played at third base, excluding shortstops and second basemen*. Leaving these guys out isolates a special group of third baseman that, I think, captures a lot of what we may be trying to be looking at weight. By excluding players who never played shortstop or second base we get the Sandoval types. The subclass of third basemen we have created is those whose major league defensive spectrum topped out at third base. These are mostly guys who perhaps moved off short or second early in their minor league.

*Excluding second basemen makes this slightly different from the aging curve I presented at Vince Gennaro’s Diamond Dollars Case Competition a couple days ago.

With our sample in mind, I constructed an aging curve of the ratio of games played at third to total games played, using the delta method. If you are not familiar with the delta method, it is a common way of measuring player aging. To summarize: You start by taking couplets of players who played consecutive years; from there, you can look at each player's "delta", or the difference in the metric of interest from, say, the age-27 to -28 season; average all of these values (weighting appropriately), and you have constructed an aging curve. There are implicit issues of survivor bias when using the delta method, but I contend that is actually okay for our purposes and more of a feature than a flaw. To be included in my calculations, a player had to meet the above criteria -- that is, they are strict third basemen. In addition, they had to play third base in at least 50% of their games in year one of the couplet. Without further ado, here is the curve I constructed both in chart and table form.

The curve shows a sharp but leveling decline in ratio of games played at third. The curve is consistent with the theory behind the defensive spectrum. Since we exclude shortstops and second basemen, the likeliest candidates to move onto third mid-career, we see a consistent drop at nearly every interval. The leveling of the curve around age 32 is likely due to the survivor bias I mentioned before. That is, players who have made it to 32 and remained regular third basemen are likely still there because they are exceptional third basemen. I consider this a feature of the curve because if we were considering an age-32 Pablo Sandoval who was coming off a season where he played 90% of his games at third, I would be far less worried about him remaining there when he is 33. However, because Sandoval has only so far shown he can make it to age 28 while staying at third, the probability he is still there when he is 33 is much less certain.

To forecast Sandoval’s defensive value, we may index our calculations of peak percent to 100% in the age-27 season. From there, we can estimate the rate of decay for players making it up to their age-27 season while playing most of their games at third.

And there we have it. Here is a pretty good guess at how much third base we can expect Sandoval to play through the rest of his career. Let us assume Sandoval is worth 15 runs above replacement at third base. If we place him at first base and consider the appropriate positional adjustments his value at first comes out to be exactly 0 (the adjustment is +12.5 for 3B and -2.5 for 1B). Now we can weight each year moving forward appropriately towards third and first base while also considering normal defensive aging of about one run a season.

Thus, given some rough estimation, we can expect some pretty aggressive aging in Sandoval’s value, since the likelihood of him moving off third base by his age-32 season is roughly 50%.

Sandoval is a premier player, and will likely get a large and well-deserved contract this offseason. However, as the Panda ages, we can expect a good chunk of his value -- his defense at third -- to diminish, solely due to the fact that it is hard for strict third basemen to stay at third through their mid thirties. If Sandoval can manage his body and make it through his age-32 season as a third baseman, he will have a good chance of staying there. Teams such as the Giants, who have first base locked up and no DH to speak of, might be a little more hesitant to offer Sandoval a lengthy deal. If we are talking about anything longer than a six-year deal, the question is not if Sandoval will move off third, but when.

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All stats courtesy of Sean Lahman and the Lahman Database.

Daniel is a junior at Colby College and contributor to Beyond the Box Score and The Hardball Times. You can follow him on twitter @dtrain_meyer.