No one seems to be exceptionally excited about the Jhonny Peralta acquisition. Responses seem to vary from “I hate it” to “it’s okay.” But what if it had been Stephen Drew that the Tigers had traded for? I’m confident that there would have been a near unanimous response of “LOVE IT!” So what is it that separates Stephen Drew from Jhonny Peralta (besides ten months in age)?
I’m going to look at this question from a purely statistical standpoint. I’ll use wOBA and UZR to assess their offensive and defensive abilities and then combine the numbers into runs for a single number comparison (this will be similar to the other shortstop posts I’ve done). When assessing defense, I’ll only consider Peralta’s numbers from his seasons at the shortstop position, hopefully this will give us an “apples to apples” comparison.
I’ll start with their respective career numbers. Stephen Drew has been pretty much league average at the plate for his career with a .331 wOBA. Jhonny Peralta has been a shade worse at .326. The difference in offensive potential between these two numbers is 2.8 runs in 650 plate appearances (approximately one season). On the defensive side, Drew has been about 7.2 runs below average (per 1300 innings) according to UZR. Peralta has been about 6.1 runs below average for his career. Obviously, this difference is about 1.1 runs in favor of Jhonny. So, according to their career offensive and defensive metrics, Drew would add about 1.8 runs of value more than Peralta would over the course of the season. Whoop-de-doo. (More after the jump)
But career numbers isn’t necessarily the best way to determine relative values of two players. Let’s look at the recent history of 2007-2010 (three years plus this season) to see if we can get a different look at these guys. On offense, the three year difference is quite small. Drew leads Peralta by 0.002 wOBA points, which is good for 0.8 runs of offense in a season. On defense, Drew has been 6.5 runs below average (again, per 1300 inning season), and Peralta has been 5.0 runs below average (only considering his time at shortstop). Put these numbers in a blender, and we’d expect Peralta to contribute 0.6 runs more than Drew over the course of a full season. Another whoo-de-doo.
We do see a big difference, however, when only considering this season’s numbers. Drew has had a big advantage on offense, and he’s also having one of his better defensive seasons (according to UZR). Drew leads Peralta by .022 wOBA points (12.4 runs per season), and 11.7 runs of UZR (I had to use Peralta’s 2007-2010 UZR average since he didn’t play short this season for Cleveland). That’s good for a total advantage of just over 24 runs (2.4 wins) for Stephen Drew. This is the most significant difference we’ve seen between the two players, but unfortunately it’s probably the least statistically significant one. One standard deviation of wOBA due to random variation is .026 points in 380 plate appearances (and we’re showing a .022 difference). UZR is also notorious for giving poor readings in small sample sizes (less than three or four seasons worth of data).
In general I tend to trust either career numbers or a three year average over a single season’s worth of data, but I’m not going to tell you which of the data sets you should go with. I think Peralta could handle the shortstop position in an everyday role, but his disappearing bat is a big concern. If he can pick up the pace at the plate and even approach his career numbers, he’d be a valued member of the 2011 version of the Tigers. For as similar as their career numbers are I’m surprised that there’s been so much clamor for Drew and so little interest in Peralta. Maybe I’m off base?