According to Baseball Prospectus' defensive efficiency metric—which measures how often balls in play are turned into outs—the Red Sox just aren't getting the job done.
Theo Epstein and the rest of the organization have been adamant about keeping a solid defense on the field. And they have stressed it again this season, at least in terms of personnel. But the team just hasn't been getting to balls as often as they have the passed few seasons.
They are currently 27th in the Majors in regards to the metric (DE), and 13th in the American League.
But again, the personnel, it is there.
In center, Jacoby Ellsbury roams full time and has not been poor by any means. However, his 3.2 UZR/150 (3.2 runs saved per 150 games), has been far from great.
Ellsbury makes spectacular plays, and doesn't make many mistakes on the defensive side of the ball. But the young CF is still learning how to run routes, and has been adjusting to the ballparks at this level.
But Ellsbury is the victim of a small sample I would assume. The sample size after 50 games is decent for offensive numbers, but much less reliable when it comes to defensive metrics, which are not necessarily suspect, but not quite as reliable as offensive metrics in general.
So this information should be absorbed, and an opinion should be formed, but that opinion should be taken lightly after only 50 games, in regards to a defensive metric.
Kevin Youkilis, JD Drew, and Dustin Pedroia have all been good as far as defense is concerned. None of the three are on pace to save fewer than four runs above average, which is obviously a very good thing.
The largest problems are at the most obvious positions.
Julio Lugo and Nick Green have combined to give the Red Sox below-average defense at the most important position, outside of the catcher. They both have struggled, combining for 15 errors, and both have posted sub-par UZR's. We see these "struggles" on a daily basis, and in this case it has translated into some hard-nosed evidence.
Jason Bay, even though he may be better than Manny, is not a good defender. Bay overall has been great, but his -11 runs "saved" per 150 games is, like the Shortstops, sup-par. Bill James once made it clear that there may be some flaw in the metrics because of the monster, but Bay has never been a great defender to begin with. But the bat makes up for that, definitely.
Not so obvious a flaw, but Lowell may too be the victim of the small sample. Because, ever since Lowell has arrived in Boston, his defense has been quite good. But he IS older. 35 years of age. So range will be lost as one ages, and this may be no exception when it comes to Lowell.
We don't as fans like to admit that players lose something, especially "fan favorites." But it happens to everyone. Although, I expect Lowell to improve on this side of the ball, because as he mentioned, he was gaining strength as the season progressed. And with that torn labrum, it only makes sense that his lateral movement will improve.
Since two reliable metrics are more valuable than one, let me quickly point out that the Red Sox as a team are 25th in UZR. So both metrics—UZR and Defensive Efficiency—say pretty much the same thing, and that is that the Red Sox defenders are tracking down far too few balls off of the bat.
But there is a catch. That dreaded variable that so many often ignore.
And that is Red Sox pitching. As Rob Neyer always states, "What happens to balls in play is essentially luck."
But the team has allowed line drives a higher percentage of the time than all but five teams in baseball. And since line drives fall in roughly 75 percent of the time, then naturally, it will be more difficult for defenders to track down these balls.
In 2008, the Red Sox were fifth in "Efficiency," but also allowed the fourth lowest percent of line drives. Meaning that defenders didn't have to track down hard hit balls as much as most other defensive units did.
And that does matter.
With an improvement in pitching will come an improvement in the defensive numbers. Because like I said, the personnel is there, and hopefully will even get better if Lowrie can return healthy enough. Because even a slightly less mobile Lowrie might do a better job than our SS by committee that is featured now.