Denard Span’s Defense

So it is now officially the offseason which is probably my least favorite time of the year. I’ve been very strong in my opinion that every trade proposal is stupid, especially the ones that are executed by MLB teams (thanks again for Doug Fister Detroit). Beyond the simple acknowledgement that the Nationals are currently missing a starter at second base or third base and will need some new players to replace the ones leaving there isn’t much more analysis one can do until an actual move is made. So until then I’m looking elsewhere for writing.

Which leads me to the actual point of this post, Denard Span’s defense. You’ll notice this post is generically titled, I don’t want to give away any spoilers as to the conclusion. As you probably know Span was just named a finalist for a Gold Glove award for the National League’s best center fielder. And one of the constant criticisms all season from Nats fans were about how criminally low Span’s defense was being rated by the defensive runs above average displayed on FanGraphs, checking in at -2.4 runs to end the season. With that in mind I read my friend Jason Wojciechowski’s piece on the similarly talented Coco Crisp for the A’s who also saw his defensive numbers take a dive this year. Inspired I took a deeper dive into Span’s numbers and present my findings thusly.

To start with we’ll take a look at that pesky FanGraphs number that most people are likely most familiar with. That number is a combination of UZR, a statistic developed by Mitchel Lichtman that at its root measures how well a player fields balls hit in specified zones on the field and converts it to runs, and a positional adjustment that is meant to level out all fielders regardless of position. For Span he gets a boost of 2.2 runs for playing a premium defensive position in centerfield, but saw his UZR drop from 10.2 runs in 2013 to -4.7 runs in 2014.

OK, so that’s definitely bad, but is it accurate? To start with defensive numbers often need a larger sample size than just a single year to ensure accuracy considering how ratable plays a fielder sees each season. For example in 2014, Span saw just 401 balls in play that were tracked by Baseball Info Solutions, which compiles the play data that makes up UZR. That’s just not enough to get a fully accurate picture and it’s suggested that one take three years of UZR to make an accurate judgement. But we want to know more about Denard Span’s defense this season, not when he was still with the Twins. Luckily we have three other advanced defensive statistics we can compare to, DRS, which also uses Baseball Info Solutions data, and Total Zone and FRAA, both of which use regular play-by-play data. And for extra context let’s take a look at both of Span’s years in DC.

statsSo unlike in the case of Crisp there is some disagreement between the various measures about Span’s defensive value this season after a fairly good accord in 2013. While the play-by-play numbers stayed nearly exactly the same in 2014, Span saw his BIS-based stats take a huge dive. And that has a big effect on his reported value as well. By FanGraphs’ WAR, which uses UZR, Span was worth 3.8 wins, eighth best among centerfielders. But by Baseball Prospectus’ WARP, which uses FRAA, Span was worth 5.7 wins, third best among centerfielders.

Without more information into the specifics of the algorithms that produce these various statistics, which are not publicly available, we can’t really know for sure where the disagreement is coming from. It could just be an issue of a small sample size, but the play-by-play stats are also based on the same small number of plays. It could be an issue of human bias from BIS, but overall UZR and DRS are touted by many to be the more accurate measures as they capture a more discrete data set. It could just be that Span has pulled a fast one on Total Zone and FRAA. We just don’t know.

What we do know is that Denard Span played centerfield for the Nats and by some measures was apparently good and by others was apparently pretty bad. And we know that his defensive value is probably somewhere among the various statistics, but it also might not be. And we know that Span was recognized as a Gold Glove finalist, which is pretty cool despite the many cases where the award’s value has been questioned. It’s up to the individual to decide what this all means to them. Personally, I like to think Span’s defense is pretty dang good, even if he is not one of the very best in the league.

In conclusion I leave you with the closing words to the Coen Brothers’ underrated film Burn After Reading.


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