From http://actasports.com/sow.php?id=203

The most significant discovery of my career

March 12, 2009

About two weeks ago The Fielding BibleóVolume II went to print. Since then, as I've been studying some of the data in the book preparing for interviews, I came upon a discovery that was truly amazing to me. The most amazing, and significant, discovery of my 25 years in the baseball analysis business.

The key mission of the second volume of The Fielding Bible was to translate all of our new defensive methods into one common number that would be understandable by everyone. That number is Defensive Runs Saved. How many runs does a player save for his team defensively?

We look at each player individually. We then do a team summary by adding up all the individual players. How many runs does an above-average defense save compared to an average team? The team with the best defense in baseball in 2008 was the World Champion Philadelphia Phillies. By combining all of our defensive methods, eight different methods across the nine positions in baseball, we estimate that the Phillies defense saved 78 runs. Using the rule of thumb that 10 runs is equivalent to one win, that's eight wins. With an average defense, the Phillies wouldn't have had even a sniff of the playoffs.

The worst defensive team in baseball in 2008? The Kansas City Royals. Their defense cost them about 48 runs relative to the average team. Comparing the Phillies and the Royals, the difference between the best and worst defensive teams in baseball was about 130 runs.

Now, remember that number. 130.

The best run-scoring team in baseball was the Texas Rangers with 901 runs in 2008. The San Diego Padres were the worst with 637 runs. That's a difference of about 260 runs.

Here's the discovery, and I found it because the numbers just jumped out. The 130 difference in runs saved on defense is exactly half of the 260 difference in runs scored. That's exactly half. The implication is that defense is worth about half as much as offense.

That's a lot higher than I would have guessed, and a lot higher than I think most people would guess. But the numbers are remarkably consistent from one year to the next:
Code:
Year 	Best to Worst Offensive Difference 	Best to Worst Defensive Difference 	Defensive Spread
as Percentage of Offensive Spread
2008 	264 	126 	48%
2007 	295 	141 	48%
2006 	241 	114 	47%
Everyone realizes that defense is important, but it's never been quantified. Now we have the first way to quantify it. It's not necessarily the best way, and there will be more to come on this issue. The 50% figure is more of an indicator than an exact number, but it just jumped out at me and I wanted to share it with you.