Khalil Greene’s Defense

Yesterday, we spent a couple of posts talking about how defensive statistics have to be handled a bit differently than offensive statistics. Today, we’ll use a current event transaction to delve into this a little bit further.

Yesterday, the Cardinals acquired Khalil Greene from the Padres to fill their void at shortstop. The Padres are in cost cutting mode, and didn’t want to pay Greene the $6.5 million he was due in the last year of his contract. The Cardinals wanted to upgrade from Cesar Izturis, and are hopeful that Greene can provide significantly more offensive value now that they’re freeing him from the clutches of Petco Park.

However, Tony LaRussa has always been a defense first guy at shortstop. From Mike Bordick to Royce Clayton, LaRussa wants his shortstops to defend well, and if they hit, that’s a nice bonus. Clearly, the Cardinals wouldn’t have acquired Greene had they not been convinced that he could handle playing shortstop at a level satisfactory to LaRussa’s desires. So what do we make of Greene’s defense?

Well, his +/- ratings from 2006 to 2008 go from +13 to +7 to -4. If each year was considered an isoloated result, we’d conclude that two years ago Greene was one of the game’s best defenders at the toughest position to field but had fallen off substantially since then, to the point of being below average now.

Was Greene a terrific fielder who has since deteriorated to the point of being a minor liability? Maybe, but because of the variance in single year metrics, we certainly can’t state that with any kind of confidence. However, if we view each year as a data point, we’d find that the mean of his defensive value over the last three years is between +0 and +5, depending on how much weight you give to the most recent data points. Because of the larger sample, we can state with significantly more confidence that Greene was something like a +0 to +5 defender over the past three years, which would allow us to make a pretty decent projection for what he’ll do going forward.

As with all projections, a multi-year weighted collection of data will be more accurate than if you simply use the past year’s results and take them as the gospel truth. Every projection system worth it’s salt incorporates regression over several years to determine future output, and with Greene, that’s exactly what we have to do with the defensive data. The -4 rating from 2008 is a data point, but whether it represented an actual decline in his ability or not, we just don’t know. There’s too much noise in the data to support that kind of claim.

So, Cardinals fans should expect Greene to be something like a league average defensive shortstop or maybe a tick above. Toss in enough gap power to overcome his low OBP, and St. Louis just picked up a +2 win player for 2009. Considering his salary only values him at just over 1.25 wins, the Cardinals are getting a bargain for their money. Unless the PTBNL in the day is a significant prospect, we’d have to call this a good move for St. Louis – even with Greene’s -4 +/- score from 2008.

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Dave is the Managing Editor of FanGraphs.

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