Defense is a tricky thing. It's hard to grasp the value of, say, an Adrian Beltre at 3rd for a lot of fans. We understand that an elite defensive third baseman is better than a bad defensive third baseman, but a lot of the time it's hard to determine where the pitcher being good ends, and the defense being good begins. As much as UZR tries to turn defense into numbers, and then numbers into runs, defensive metrics are by far the least trusted of all baseball stats both by the pro-stat and anti-stat crowds alike.
There are some cases, though, which give us some more tangible results. To keep things simple, last year the Red Sox were a bad defensive team. This year, they're one of the best. In 2007, the Rays were a bad defensive team. In 2008, they were one of the best. And luckily enough, they kept their starting pitchers largely the same for us. Here's a few numbers after the jump.
| ERA (2007) | ERA (2008) | K/9 (2007) | K/9 (2008) | BB/9 (2007) | BB/9 (2008) | BABIP (2007) | BABIP (2008) | |
| Edwin Jackson | 5.76 | 4.42 | 7.16 | 5.30 | 4.92 | 3.78 | .351 | .301 |
| Scott Kazmir | 3.48 | 3.49 | 10.41 | 9.81 | 3.88 | 4.14 | .341 | .275 |
| James Shields | 3.85 | 3.56 | 7.70 | 6.70 | 1.51 | 1.67 | .292 | .292 |
| Andy Sonnanstine | 5.85 | 4.38 | 6.68 | 5.77 | 1.79 | 1.72 | .329 | .312 |
So that's something. Of the 4 main holdovers from the 2007 Rays rotation, only one of them had a worse ERA than in 2007. And that was by .01. Of those 4, 3 of them had noticeably worse peripherals. The difference may seem somewhat small, but for Andy Sonnanstine alone, that's 32 runs. And the kicker is that the Rays are the weird team that tends to underperform their defensive numbers, as compared to, say, the Reds, Mariners, Giants, or Tigers, who make up the rest of the top-5 UZR teams and tend to have the lowest BABIPs against and ERA-FIPs deep in the negatives. Here are the team stats for the Reds and Tigers, who made a similar transition last year:
| UZR | ERA | BABIP | ERA-FIP | |
| Reds (2008) | -42.3 | 4.55 | .321 | .01 |
| Reds (2009) | 52.6 | 4.18 | .288 | -.45 |
| UZR | ERA | BABIP | ERA-FIP | |
| Tigers (2008) | -39.1 | 4.91 | .307 | .12 |
| Tigers (2009) | 43.6 | 4.34 | .298 | -.18 |
If the Great American Ballpark isn't enough of a bandbox for you, how about Arlington?
| UZR | ERA | BABIP | ERA-FIP | |
| Rangers (2008) | -51.7 | 5.37 | .322 | .53 |
| Rangers (2009) | 32.5 | 4.38 | .294 | -.10 |
Just some food for thought.