A few of the comments in my earlier post suggested that the value of defense is somewhat ephemeral, that it isn't something that really can be proven or can improve much except on the margins.
As a counter-point, I'd encourage you to look at the Tampa Bay Rays.
Offensively, the Rays are the same team this year, when they won the A.L. East, as they were last year, when they had the worst record in baseball. In 2008, the Rays scored 774 runs. In 2007, the Rays scored 782 runs.
The improvement by the Rays between 2007 and 2008 has been in the area of run prevention. The 2007 Rays allowed 944 runs...the worst total in baseball (worse, even, than the 2007 Rangers). The 2008 Rays allowed 671 runs.
That's a swing of 273 runs. Now, that has to be the pitching, right? I mean...the defense could have improved some, and contributed a little bit...but that improvement is mostly because of Scott Kazmir and Matt Garza and James Shields and those guys. Right?
Apparently not. Let's compare peripherals:
|2007||2007 rate||2008||2008 rate|
The Rays in 2007 were the best in the A.L. in striking batters out, and were near the bottom of the league in walking batters and allowing homers.
The Rays in 2008 were 4th best in the A.L. in striking batters out, and were a little below average in walking batters and allowing homers.
And the Rays went from allowing the most runs in the A.L. to allowing the 2nd fewest in the A.L. That's not a change that can be explained by the improved peripherals.
There was improvement in the walk and homer rate, improvement that would more than offset the decline in the strikeout rate. But still 33 fewer homers allowed, and 42 fewer walks, doesn't explain a savings of 273 runs. That's over a run and a half per game.
What's the explanation, then? The 2008 Rays allowed 1443 total hits. The 2007 Rays allowed 1649 hits.
The 2008 Rays had a BABIP of .280, the lowest in the A.L.
The 2007 Rays had a BABIP of .332, the highest in the A.L.
That's why the Rays went from cellar dwellars to first place in one season. The pitching improved, absolutely...but if the Rays play defense like they did in 2007, they are still a sub-.500 team.
The single biggest factor in the Rays' improvement from last year was going from the worst defensive team in the league to the best defensive team in the league.