

Long before fantasy leagues and Moneyball, baseball players, managers and fans embraced statistics. Of course, common stats like batting or earned run average are relatively easy to quantify because there are a only finite number of possible outcomes in hitting or pitching. But creating a model that accurately reflects the fielding performance of individual players is a much greater challenge.

For one thing, fielding is a more continuous aspect of the game, so there's an enormous amount of data to analyze. And that requires developing new statistical methods.

This week at the AAAS conference in Boston, Shane Jensen of the

University of Pennsylvania's Wharton School presented a method he developed called the Spatial Aggregate Fielding Evaluation

(SAFE).

Jensen's method uses a probability model to fit a smooth curve for entire teams, particular positions or individual players.

So far the model has produced some surprising results. For example, it might stand to reason that running backward to catch a fly ball might be more difficult—and therefore have a lower probability of success—than running forward.

But in fact the opposite is true. The important variable, Jensen says, is actually the ball's hang time in the air. It also turns out that fields with a non-standard shape—like Beantown's own Fenway

Park with the Green Monster looming in left field—don't make as big a difference as people might think.

And by analyzing four years of high-resolution data from Baseball Info Solutions (BIS)—containing information on some 120,000 balls in play per year—Jensen was able to rank the best and worst fielders at each position based on the number of runs saved or cost. The results showed what Derek

Jeter-haters have long suspected: that with and average of 13.81 runs lost per season, he's a lousy short stop. Meanwhile, his teammate

A-Rod is one of the best in the league with and average of 10.4 runs saved.

But what the model doesn't—and can't—take into account are intangibles like charisma and grace. As the influential baseball writer Bill James once wrote: “Hitters are judged on results; fielders, on form.”

Image: flickr/Wally Gobetz