Defense May Be More Important Than You Think

Via BBTF, John Dewan has made an interesting discovery:

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:

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.

The impact the above has on you greatly depends on your preconceived notions on the importance of defense.  I think it's reasonable to assume, however, that most people don't consider defense to be about fifty percent of the value of offense. As John stated, this may not be the best way to actually quanitfy the relationship, but it's the first way and hopefully a launching point to narrowing the relationship down even further. What interests me is being able to calculate the value of a player in runs that uses a combination of offense and defense.  Assuming this roughly fifty percent to be accurate, combining half of a fielders UZR/150 with their Runs Created Above Average (RCAA) would seemingly give a greater picture of the players overall value. Looking at a defensive position like shortstop for 2008, Jimmy Rollins was the best in the majors with a 15.9 UZR/150.  Rollins also had a RCAA of 11.  Combining the 11 RCAA with half of the 15.9 UZR/150 gets us a net of about 19 net runs above average. Applying it another way, 2007 NL MVP Jimmy Rollins had a net runs above average of 32.5 (30 RCAA + (.5 x 4.9 UZR/150).  Runner up Matt Holliday had a net runs above average of 62  (55 RCAA + (.5 x 14.1 UZR/150).  Rollins received great praise for this defense and offensive prowess at a defensive position.  Looking at those numbers, Holliday was clearly the more valuable player by quite a margin.