The Red Sox and Yankees are the two most fearsome offenses in baseball this season, but in Game 1 of the ALCS, it became clear that their defenses are not on the same level. Yankee left fielder Hideki Matsui missed two catchable fly balls in the late innings, the second of which fell in for David Ortiz’s eighth-inning triple that brought the Sox within one run of the Yankees’ long-since disappeared eightrun lead. The following inning, Red Sox leftfielder Manny Ramirez couldn’t get back in time to catch Bernie Williams’s double, which plated two crucial insurance runs.

The defensive miscues, while ugly, shouldn’t surprise anyone: These are two teams built with an offense-first mentality. What might be surprising, though, is that the Red Sox enjoy a comfortable lead in fielding ability, and did so even before the defense-oriented acquisitions of Orlando Cabrera and Doug Mientkiewicz at the July 31 trade deadline.

One of the most basic ways to look at team defensive performance is a statistic called Defensive Efficiency, which calculates the ratio of balls fielded by the defense to the total number of balls in play. DE is better than a statistic like fielding percentage because it does not punish teams for making errors on plays that other teams let fall for clean hits: You can’t make an error on a ball you can’t reach. As an added bonus, the inconsistency of official scorers from park to park is removed from the equation.

For example, take two hypothetical shortstops who, over the course of the season, have the exact same 500 balls hit to them. The first shortstop lets 100 of these balls bounce past or fall in for hits. The second player lets 90 of these go for hits, gets to 10 balls the first shortstop didn’t, but makes errors on them. Both shortstops have performed equally well at the job of turning balls hit to them into outs, but one has a perfect fielding percentage while the other does not. DE rates both of these players equally.

Looking at New York and Boston, two distinctly different defensive teams emerge. The Yankees start out with a lead because Yankee Stadium is easier to play defense in than the average park, despite the large outfield power alleys. But adjusting for their friendly home field, the Yankees rank 25th in the majors in DE.

The Red Sox, on the other hand, place eighth in the majors in DE this season, meaning they do a much better job of converting chances into outs. Fenway Park is a much more difficult place in which to play defense because of the odd and expansive centerfield and the indefensible balls hit off the Green Monster. This fact makes the Red Sox’ fielding performance all the more impressive.

Just before the trading deadline in late July, the Red Sox traded away Nomar Garciaparra for Cabrera and Mientkiewicz, saying they wanted to improve their defense. Despite dire predictions, the trade worked out for the Sox in the final weeks of the season. Their DE improved markedly after the trade; they allowed a .315 average on balls in play before the trade, but only .287 after.

That improvement, however, was not due to the new arrivals: Cabrera has been the team’s worst defender since the trade and Mientkiewicz has seen little playing time. It was the rest of the Sox team that improved as the season moved on.

Baseball Prospectus has devised a metric called Fielding Runs to evaluate individual players’ defensive performance. Like DE, FR does not punish a player for errors but rather rewards him for making plays that others do not. FR adds up all the potential hits the player takes away from the opposition and then calculates the total number of runs the player saved his team as compared to the average defensive player at that position this year.

According to FR, the Yankees feature just two above-average defenders this year: Alex Rodriguez and Derek Jeter. When the Yanks traded for Rodriguez in the off-season, many argued that Jeter should move to third base because of Rodriguez’s superior defense. While A-Rod has saved more runs for the Yankees at third than Jeter has at short this year, Jeter has had his best defensive year ever by a wide margin.

Jeter has averaged 15 runs below average per season at shortstop for the past nine years, making him one of the worst defensive players in the majors. But this year he is two runs above, an unprecedented turnaround for a player as established as the Yankee captain. Clearly, some of the credit – though it’s hard to say exactly how much – should go to the Yanks’ new man in the hot corner, since A-Rod reduces the amount f space Jeter has to cover in the field.

It would appear on paper that the Yankees have also bolstered their defense significantly at first and second, but that hasn’t been the case. Considering second baseman Miguel Cairo’s struggles in the field, it’s amazing that he is nonetheless a small upgrade over Alfonso Soriano. And despite appearance to the contrary, John Olerud and Jason Giambi have posted very similar FR totals over the past two years. All told, the Yankee defense is better than it’s been in the recent past, but not by much; interestingly, Jeter’s turnaround accounts for the bulk of the team’s slight defensive improvement.

Jeter’s counterpart in this series, Cabrera, was identified by the Red Sox as their defensive savior, but his defensive play has actually cost the Sox six runs down the stretch. Though Cabrera hasn’t been the same injury risk as Garciaparra was, his fielding certainly hasn’t made up for the difference between the two at the plate. Making matters worse, there’s a gaping hole on the other side of second, where Mark Bellhorn was nine runs below average fielding this year.

Interestingly, Ramirez’s notoriously porous defense in left comes out as slightly above average in FR in 2004. This is due to several factors. Most importantly, the sluggish Ramirez plays in the smallest right field in the majors, allowing him to field a disproportionate number of balls hit to left that don’t make it to the Monster. Also, playing next to a top centerfielder like Johnny Damon allows Ramirez to shade slightly closer to the left field line since Damon can cover so much ground in left center. Finally, left field is not a position that is occupied by many top quality defenders. Players like Barry Bonds, Adam Dunn, and Geoff Jenkins don’t set a very high standard for defense.

Mientkiewicz has a reputation as one of the premier defensive first basemen in the league, built mostly on a spectacular 2001 season. Though he’s been very good since then, the difference he makes with the leather is nothing close to the difference Kevin Millar makes up for with the bat. Sitting Millar for Mientkiewicz only makes sense for the Red Sox if Millar isn’t likely to bat again.

Of course, the Sox’ defense may not be enough to save them from the hole they find themselves in. If they are to take advantage, it may come behind Derek Lowe, a pitcher who strikes out far fewer batters than Curt Schilling, and thus puts more opportunities in his fielders, hands. It’s a silver lining on the injured ace’s injury, though that silver looks a little tarnished for now.

This article was provided by Baseball Prospectus. The Sun will run exclusive content from Baseball Prospectus throughout the 2004 season. For more state-of-the-art baseball content, visit www.baseballprospectus.com.