Jason Bay is now average defender

Los Angeles Dodgers at New York Mets

A little over a week ago fangraphs.com updated their UZR calculations with the first batch of 2010 data. This update included some work on arm skill as well as changes for quirky stadiums including Fenway Park. This change was done to include previous seasons and now Jason Bay made one of the largest gains as his -13.8 runs value became a 1.9 value.

John Tomase decided to use this as a chance to say UZR owes Jason Bay an apology.  Let’s start with a reminder there is no chance the Red Sox are using UZR and have their own model so let’s not make any assumptions UZR had anything to do with the Red Sox failing to sign him.  Even with the changes, no stat is perfect and I’m sure we’ll be discussing the next Bay in the offseason.  Perhaps that will be Jeremy Hermida who has improved his defense in UZR coming from Florida.

Let’s see if one year of average defense data makes Jason Bay suddenly a player the Red Sox should have gone to four years at $66 million.  His WAR in 2009 increased to a very solid 5.0 worth approximately $22.3 million last year.  That is impressive and moved him up to second on the team for position players behind only Kevin Youkilis who had a 6.0 WAR.

The first question is how solid is that UZR number?  Single year data is not very solid yet for UZR and it’s currently thought you need about three years of data to find a solid average.  That causes problems here as Bay had only played one year in Fenway where he was able to be an average defender for the first time in three years.  That could be partly explained by his knee troubles in 2007 as well.

So far in New York he has been average as well, although slightly negative, but minimally.  I’m fairly comfortable saying Bay would have been average for another year or two in Fenway and perhaps no more than 10 runs negative by year four of a deal to stay in Boston.

Assuming he doesn’t enter into the “old player skills” decline and follows a normal decline in his 30′s you should expect him to total WAR numbers of 4.5, 4.0, 3.5, 3.0 as the average decline is 0.5 WAR per season.  That gives him a total of 15 WAR in the next four years, ignoring the option year in 2014.

That is nothing to ignore as 15 WAR based on the value of a win above replacement previous to this offseason would be $67.5 million, but after this offseason it would be down slightly as many players found closer to $3.5 million per win.  That would make him worth closer to $52.5.

Based on these numbers Bay is someone who might have looked better to the Red Sox as a outfield and DH option.  His fielding is obviously better hidden in Fenway Park and with Ortiz up after 2010, he could have split time at DH when on the road.

There are still the injury questions raised by the team and his skills are that of an older player where it is hypothesized that these players will decline much quicker.  I can’t find any conclusive studies on this theory, but if his strike out rate stays above 30 percent then he will not follow the decline I outlined above.

Defense was not the reason the Red Sox got cold feet with Bay in my opinion.  Health and his skill set are the largest factor in a decision not to retain him for the next four years.

Check out the new blog/podcast from frequent commenter Aaron and writer at RotoSavants.com at http://historyoftheredsox.blogspot.com/

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