When it comes to statistics, baseball is constantly evolving. For fans that either don't have time to keep up on the new stats or don't care to learn, seeing things like WAR, wOBA, and +/- can be more than a little daunting, and can reinforce any negative feelings they might have about those numbers. While you'll see a lot of references to things like that here, I realize that not everyone reading this blog likes those numbers or understands them as much as I do (and even I don't understand them to the level that some other Brewers bloggers do).
I bring this up because the inclusion of Yuniesky Betancourt in the Zack Greinke trade has been widely criticized by stat-minded Brewer fans. I got a comment yesterday asking me if I could possibly explain why so many people think Betancourt's defense is so bad. I imagine there are a lot of fans out there hearing the knocks on Betancourt's D, but are curious as to why so many people are down on him, so what I'll attempt to do is break down the numbers and explain it as best I can.
First and foremost, it's important to remember that when it comes to defensive metrics, they're still relatively primative compared to some of the offensive statistics out there. Depending on who you look at, you may see wild fluctuations in their defensive stats from year-to-year that you may not see in their offensive stats. For the most part, this is due to sample size -- a player simply isn't going to get as many defensive chances as he will plate appearances, so there's a greater chance of the statistics being skewed. As a general rule of thumb, three years' worth of defensive data is equal to one year of offensive data, and there aren't many stat analysts out there that would be comfortable judging a player based on one year at the plate.
For that reason, in most cases I see defensive stats as a way to describe what happened in the past, rather than using them to determine a player's value or predicting future performance. When a player has had bad defensive numbers AND he's failed the "eye test" -- he just looks bad out there -- I do feel more comfortable labeling someone as a bad defender.
Basically, I'm at that point with Betancourt. The stats say he's bad, and he just looks bad.
First, let's take a look at Revised Zone Rating (RZR), which is essentially the percentage of balls hit into a player's "zone" that he turns into an out. In 2010, league average RZR for qualified shortstops was 0.798 -- in other words, the average shortstop turned balls in his zone into outs 79.8% of the time (if you're worried about the average being skewed by extreme highs/lows, it turns out the median number among qualified shortstops -- Yunel Escobar's .798 -- is exactly the same). For a point of comparison, the league leader among shortstops, Brendan Ryan, was nearly 5% higher with an RZR of .844. Betancourt's RZR of .781 is below average, but far from being worst in the league -- names like Hanley Ramirez, Starlin Castro, and Derek Jeter finished below him, so at least you can say in 2010 he wasn't the absolute worst in RZR. In terms of career numbers, he's converted 1610 outs on 2060 balls hit into his zone, good for a career RZR of .782 -- not far off from his 2010 numbers.
That's about the extent of the good news for Betancourt, though. If you look at Defensive Runs Saved (DRS), which measures how many runs above or below average a player is compared to those who play the same position, things get ugly for him. The scale for DRS is simple -- "average" is 0; positive numbers are runs above average (you're "saving" runs for your team), negative numbers are runs below average(you're actually "costing" your team runs). In 2010, Betancourt was -21 in DRS. No shortstop in baseball cost his team more runs, and he was the only one to break the 20 below barrier. This isn't exactly a new trend for him...in the past three years, he's posted DRS numbers of -19, -13, and -7. He hasn't been "average" in DRS since 2006.
Similarly, Ultimate Zone Rating (UZR) measures how many runs above/below average a player is when you combine range runs, outfield arm runs, double play runs, and error runs (FanGraphs has a pretty good primer on UZR that you can find linked in their fielding stats glossary). Betancourt also largely stinks here, too. At -3.5 double play runs, -5.3 range runs, and -0.8 error runs, Betancourt's total UZR of -9.5 was the third lowest among qualified shortstops in 2010 -- only Ramirez and Jason Bartlett were worse.
Hopefully this sheds a little light on why so many people think the Brewers' defense will get worse in 2011 by swapping Alcides Escobar for Betancourt. There's a definite chance (almost an inevitability) that Betancourt will cost the team runs and hamper the effectiveness of the new rotation. Betancourt's defense is so bad, there's a chance the expected improvement in the numbers for Greinke and Shaun Marcum (due to shifting from the AL to the NL) could be nullified, or at the very least limited.