How defense affects pitching

Every year, David Pinto at Baseball Musings releases the Probabilistic Model of Range, his very good defensive metric which measures batted ball characteristics like velocity and location in order to determine how many outs teams should have made on those batted balls relative to how many outs were actually made. This year, he also gave the PMR for defense behind pitchers, which Beyond the Boxscore translated into runs and ERA.

If you doubt that defense can make much of a difference behind the pitchers, look at how the numbers ran for the Pirates. Ian Snell lost 0.63 of a run on his ERA, which would've brought his ugly 5.42 down to 4.79. Tom Gorzelanny adjustment is almost as big, while Zach Duke only lost about a tenth of a run to defense, according to this metric. Of course, looking at our pitchers' adjusted ERAs is still depressing because it really drives home just how poor our pitching staff was this year.

The other interesting thing that leaps off the page at me is that Snell and Gorzelanny, the two pitchers that induce the fewest ground balls, were hurt most by the Pirates defense while Duke, who's GB% is higher than either of the first two, saw little effect. Paul Maholm, who gets the most groundballs of the four by a pretty good amount, was actually helped by the defense this year. I guess intuitively that makes sense as the infield, save Freddy Sanchez, was actually kind of good defensively last year. On the other hand, we know there were issues in the outfield with just about everyone that played out there (we've discussed McLouth a lot, Nady consistently ranks as one of the worst right fielders by PMR, and Jason Bay doesn't usually score well either ... if you take the time to look through Pinto's data you'll see the Pirates ranked below average in all three outfield slots).

As with any defensive metrics, you can make of this what you will. Still, I think the disparity in the groundball and flyball pitchers is worth noting, if only for future reference when trying to figure out what the team is trying to do.