Here's a good article by Buster Olney about what's different about the Pirates this year:
It's not a coincidence that a handful of teams decided in the offseason to improve their respective defenses. For example, the Pittsburgh Pirates replaced Jason Bay with Nyjer Morgan and hired infield coach Perry Hill to work with the likes of Andy LaRoche and Freddy Sanchez. The Mariners traded for the underrated Franklin Gutierrez and Endy Chavez and now might have the best defensive outfield in baseball. And the Texas Rangers installed Elvis Andrus at shortstop and moved Michael Young to third.
Those three teams have improved their defense, and their place in the standings. The Pirates rank No. 1 in the Baseball Prospectus defensive efficiency ratings:
1. Pirates 0.738
2. Dodgers .727
3. Blue Jays .718
4. Athletics .708
5. Mariners .706
18. Rangers .687
Compare that with the final 2008 rankings:
1. Rays 0.710
2. Cubs 0.705
3. Blue Jays 0.704
4. Athletics 0.700
5. Red Sox 0.699
26. Mariners .682
28. Pirates 0.675
30. Rangers 0.670
If there a lesson to be learned, it might be this: The fastest route to improvement might not the addition of a big home-run hitter or a high-profile, free-agent pitcher. Rather, the best road to improvement might be to commit a team to better defense.
The pitching this season has been much improved, but not nearly as much as the change in team ERA (from 28th in the majors in 2008 to first in 2009) suggests. Actually, the change in ERA correlates very strongly with the change in defensive efficiency, which measures what percentage of batted balls a team's defense as a whole turns into outs. For several years before this one, the Pirates were terrible at this; this year, they've been downright great.
The question is whether the defense can keep this up. The Bucs are returning five starting position players from last year, plus two more guys in Andy LaRoche and Brandon Moss who started most of the time in August and September, so it's likely that the defense will slide down the rankings a bit as the year goes on, and the Bucs' ERA will slide down the rankings with it.
Still, there's something here--the infield has looked much better than last year, particularly since the first few games, when Andy LaRoche couldn't be depended upon to make even the most basic plays. Freddy Sanchez has looked much better than he did in 2008 and, first few games aside, Andy has probably been an improvement over Jose Bautista, who always looked good out there but was, at least by advanced statistical metrics, a pretty poor defensive third baseman.
The outfield defense has been very good, too. I'm still not a believer in Nyjer Morgan's hitting, but I have to hand it to him--in the field this year, he's looked like a real baseball player and not merely a really fast guy. In 2007, Morgan showed great range, but he ran poor routes--he'd run off in one direction and then dart off a different way, often taking a sort of banana-shaped route to the ball. When a ball was hit his way you were never sure whether he was going to look like Willie Mays, or Billy from Family Circus. Because of Morgan's age, the number of years he'd spent in the minors, and the fact that he looked like he'd never received a day of instruction in his life, I assumed there was no hope for him--that he'd never be more than just a fast guy.
Judging from the Pirates' first month of baseball, I was wrong. He takes better routes and is much more sure-handed now. Also, he seems to be better suited to left field, where (I wonder if) the boundary of the foul line to his right helps him orient himself. Last year, Jason Bay galloped to the gap like a Shetland with laminitis, so Morgan probably would have been an improvement no matter what, but I'm surprised by how big that improvement has been. In any case, it's high time I showed Morgan some respect. I'm still extremely skeptical of him as a starter because I think the hitting will tail off a great deal, but if he's going to play defense this well he should at least be able to carve out a decent career as a bench outfielder.