I posted this on the Cranks' site, and am repeating it here, FWIW.

DER isn't a perfect indicator of fielding. Batted ball types and zones enter into the picture a lot. The best correlation I've found between DER and the best fielding stats, such as UZR, is .50. Good, but still not enough to say that a specific team was a great fielding team.

IMO, the more proper conclusion is that great pitching teams either have great fielders, or pitchers that give up more hittable balls, or just plain luck.

Also, IMO, the best thing to do is calculate DER over a couple of years, which would at least take luck out of the equation (hopefully).

Here's a link to some analysis I performed on this:

http://www.baseballgraphs.com/main/index.php/site/article/der_responsibility/

Plus, here's my analysis of great fielding teams, with the DER caveat (and noting the Crank's previous research!):

http://www.baseballgraphs.com/main/index.php/site/article/great_fielding_teams/

Two thoughts:

Interesting that rate of conversion of batted balls to outs is the most important factor. Though, as noted by the Crank, most of these teams played in an era where BB, K & HR were much rarer than they are today. HR might become the most important factor if the study focused on a more recent time period (e.g. past decade).

It's fairly clear from Crank's study that low ERA and high DER are correlated, but there's no indication that low ERA is caused by high DER. It could be the reverse: that the best pitchers tend to induce the easiest-to-field balls (low ERA causes high DER). Causation is a tricky beast.