Inside the numbers: Defense matters

I was reading an interesting book excerpt on’s Page 2 shortly after deciding to write this week on the value of defense.

The excerpt recounts the Boston Red Sox’s 2004 trade that sent Nomar Garciaparra to Chicago for shortstop Orlando Cabrera and first baseman Doug Mientkiewicz.

The trade was criticized throughout baseball as “a .320 hitter for a pair or .240 hitters”, and general manager Theo Epstein was called crazy for trading a perennial All-Star for a pair of seemingly useless players.

But Cabrera and Mientkiewicz, both Gold Glove winners in 2001, brought something that Garciaparra didn’t – defense. Hopefully we don’t have to tell you how that trade turned out for Boston.

The so-called Moneyball era in baseball burst on the scene in the early part of the decade and with it came an emphasis on undervalued statistics like on-base percentage. But once the secret got out, every general manager in baseball wanted to stock their lineup with the next Jason Giambi, and on-base percentage was going at market price.

While the copycat general managers continued to spend their time figuring out the difference between OBP and OPS, others were on the lookout for another undervalued asset. And Boston’s seemingly unbalanced trade quietly made a case for defense.

So it’s no surprise the two teams dominating the defensive market this season are the Red Sox and the Billy Beane-led Oakland A’s. Boston is the best defensive team in baseball with just 31 errors and a .990 fielding percentage and Oakland is third with 42 errors and a .988 fielding percentage.

But the kind of defense we’re really talking about is a lot more than just catching the ball when you’re supposed to. Think of how many times an outfielder has made a diving catch in the gap with a runner on second to end the inning. Instead of a double and a run scored, a pitcher gets off scot-free.

Now imagine that same situation, but it’s a slow groundball that gets through the hole just between the first and second baseman. Chances are a better pitch was made, but the pitcher gets a run on his record.

But how do you figure out when these plays are being made? One way would be to watch every game of baseball played and use your eye to determine which balls should be hits and which should be outs.

For anyone who doesn’t have time to chart every game, there is an easier way. The world of Sabermetrics has brought us a useful statistic called Defense Independent ERA, or dERA for short. The formula was developed in 2001 by a man named Voros McCracken, and focuses the pitcher’s ERA on things he can control – statistics like walks, strikeouts, homeruns, and hit batsmen.

Much of how oddsmakers value a pitcher’s worth in based on his ERA. A tool like dERA provides a different perspective of how that pitcher is faring.

McCracken’s findings have been a contentious issue in the baseball community. Many stat gurus argue that pitchers have the ability to control their opponents’ Batting Average on Balls In Play (BABIP). While historically this is true, research has also found that a pitcher’s BABIP will deviate widely from season to season.

In short, defense affects a pitcher’s ERA. It’s just that no one’s really sure how much of an effect it has.

But these stats still give us lots to think about. Take, for example, Jake Peavy of the San Diego Padres. Peavy is just 4-8 on the season and has lost 7.57 units in his starts.

His 4.46 ERA is also one of the worst on the Padres, but how much of that should actually be attributed to Peavy, and how much of it is out of his control?

San Diego’s 42 errors tie it with Oakland for the third best mark in baseball, and the Padres’ three other full-time starters this season, Chris Young, Clay Hensley and Chan Ho Park, all have ERAs equal to or less than their dERAs.

Peavy’s dERA is just 3.22, which begs the question: Do the Padres purposely play worse when he’s on the mound, or have a few extra grounders simply found their way through the hole?

On the other side of the coin is Cincinnati Reds starter Bronson Arroyo (9-6, +3.77 units) who’s 3.12 ERA and 3.85 dERA simply don’t match up. For one, Arroyo plays on one of the worst defensive teams in baseball. Cincinnati is second last in the majors in both errors (72) and fielding percentage (.979).

And, like Peavy, Arroyo’s teammates are all on the other end of the spectrum. Cincinnati’s three other full-time starters this season, Eric Milton, Aaron Harang, and Brandon Claussen, all have higher ERAs than they do dERAs.

Is it possible Peavy, and Peavy alone, has the ability to exploit the Padres’ otherwise solid defense? And can Arroyo possibly entice his teammates to play above and beyond their defensive limitations?

We’re dealing with sports, so anything is possible. But we’re also dealing with numbers, and in baseball, the numbers rarely lie.

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