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Andrew McCutchen and Nyjer Morgan provide a big boost to the Bucs' outfield defense.

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The Pirates' trades of Jason Bay, Xavier Nady and Nate McLouth were rebuilding deals. But that doesn't mean the next couple of years have to be that much more painful than they otherwise would have been. The Pirates' defense with Bay, Nady and McLouth in the outfield was a disaster. Without Bay and Nady it's become far better, and the improvements are likely to continue now that the Bucs have replaced McLouth with Andrew McCutchen. These changes offset most of the losses the Pirates took on offense, which is one reason why the Pirates' 2009 W-L record is practically identical to their 2008 W-L record before the Bay and Nady trades. So even though the Pirates got back prospects in these deals, they may not have made their 2009 team that much worse.

Just a warning: this article uses a ton of stats, much more than I usually use. If that's not something you're comfortable with, feel free to skip to the last few paragraphs. Or ignore this article entirely; there will be a new one in a few hours.

Let's begin with offense. I'll use Baseball Prospectus' Value Over Replacement Player statistic as a quick way to measure, in runs, how much each player contributes. VORP calculates a player's value relative to others who play his position and assigns a run value based on comparison to the typical backup or AAA player at that position. It does not factor in defense.

In all cases, I'm looking at numbers from the entire season. The 2009 numbers are through Saturday's games.

Bay, Nady and McLouth obviously made enormous offensive contributions to the Pirates in 2008, and Bay kept hitting after being traded to Boston.

The four players the Bucs traded have been far less valuable in 2009 than they were in 2008. Of course you'd expect their collective VORP to be lower than in 2008, since the 2009 season isn't over and VORP accumulates over time, but even if you multiply their 2009 total by three (since about a third of the season is now over), they're only a little more than half as valuable as they were last year. Bay has been better, but McLouth has been markedly worse, and Nady and Marte have done nothing. Of course, Nady's injury wasn't inevitable and might not have happened if he'd stayed with the Pirates, but then it also isn't inevitable that Bay would have stayed healthy if he hadn't been traded.

Still, compared to what Bay, Nady and McLouth's replacements have done, 31.4 offensive runs above replacement is quite a lot:

(BP's projection system, PECOTA, predicts that McCutchen will be 6.6 runs above replacement this year.)

On the surface, there's quite a gap between what the old guys and the new guys, even considering Nady's injury. And we feel that in the games--the Pirates just don't hit homers anymore.

And yet, even after today's loss, the Pirates are on pace to win 75 games, well above their annual total of 67. True, they played most of those games with McLouth, but they didn't have Bay or Nady for any of them. And although the Pirates collapsed badly down the stretch in 2008 after the Bay and Nady trades, this year they're playing about as well (26-30 for a .464 winning percentage) as they did in 2008 before the trades occurred (50-58 for a .463 winning percentage as of July 30). How are the Pirates doing it?

The simplest explanation is to credit the pitching, and that's certainly at least partly fair, but I don't think that tells the whole story.

The Pirates' team ERA this year is 4.31. Last year it was 5.10. But if you look at their FIP ERA, which calculates the ERA you would expect the team to have based on pitcher-controlled outcomes like strikeouts, walks and homers, the two figures are much closer: 4.62 this year, compared to 4.84 last year.

When a ball is put into play, it's largely out of the pitcher's control. So a lot of the Pirates' improvement in ERA has come from improvements in balls in play, which the pitcher really doesn't have much to do with. There are some things about balls in play a pitcher can control somewhat, though, particularly line-drive rate, ground ball rate and fly ball rate. So let's look at those. (And I warn you, there's a lot of statistical huffing and puffing here, mostly to make sure we're being fair about the defensive efficiency statistics that I'll present in a few paragraphs.)

Pitchers do have a fair amount of control over whether their balls in play go for ground balls or fly balls, so let's look at those. The Pirates have allowed about the same percentage of ground balls in both 2008 and 2009. They've allowed a greater percentage of fly balls in 2009 than they did in 2008. Or, to put it a little differently, they've replaced some line drives with fly balls.

The 2008 Pirates had a 21.4% line drive rate, fourth-worst in the majors. In 2009, the Bucs' 18.8% line drive rate is 15th-best in the majors.

Obviously, hitters tend to have a very high batting average on line drives, which explains some of the gaps between the pitchers' expected and actual ERAs in 2008 and 2009. But it doesn't explain everything.

2.6% fewer of the Pirates' balls in play have gone for line drives this year.  Pirates pitchers have allowed a .696 batting average so far this year on balls in play that were line drives. (That sounds alarming, but it's relatively normal or even a bit low.) They've allowed a .142 average on fly balls that weren't homers. 

.697 - .142 = .555, and if we multiply .555 times 2.6, we get 1.443, which is the percentage of batted balls that would likely turn into hits if the 2009 Pirates reverted to the 2008 percentages of fly balls and liners they allowed. 

Baseball Prospectus' Defensive Efficiency stat measures the percentage of batted balls a team's defense turns into outs. In 2009, the Pirates' Defensive Efficiency is .711, third-best in the majors; in 2008, it was .675, third-worst. (For context, that .675 figure is much more typical of recent Pirates defenses. In both 2007 and 2006, their defensive efficiencies were .674.)

So based on what we found about the 2008 and 2009 Pirates' line drive rates, let's subtract 1.4% from their 2009 defensive efficiency (that's the "1.443" two paragraphs above). I do this because some of the Pirates' improvement in Defensive Efficiency has to do with their pitchers allowing fewer line drives. So .711 - .014 = .697.

.697 is still much, much higher than the Pirates' 2008 defensive efficiency of .675. In fact, even a .697 defensive efficiency would give the Pirates a squarely middle-of-the-pack defense, far better than the ones they've had the past several years that have ranked near the bottom.

My point here is that a big chunk of the Pirates' apparent improvement in pitching is actually the result of improvements in defense. The Pirates' pitchers are better in 2009 than they were in 2008, but they're getting a lot more help than they've gotten in the past.

There are a number of factors that have affected the Pirates' improved defense (Freddy Sanchez's improved health and Andy LaRoche's improved play are among them), but the vast majority of the improvement has come from the outfield.

One of the best defensive stats is UZR, which assigns each player a run value based on outcomes in various "subzones" he's responsible for covering.

Let's compare 2009 Pirates outfield UZRs to 2008's. (These are the players' stats for the entire year, even when they were traded.)

Now, you can express skepticism over UZR if you want, and in fact it's wise to be somewhat skeptical of UZR figures that only reflect a couple months of the season, because they're subject to sample size issues. But this is probably the most respected defensive metric around. And it confirms a lot of what the balls-in-play data tells us, which is that the Pirates have benefited from a much better defense in 2009. As I mentioned, some of that has to do with improvements in the infield, but as UZR suggests, it's really the outfield that has improved, and it's gotten better to such a great degree that it largely cancels out the large difference between the departed players' offensive production and the new ones'.

I'm sure you've noticed that UZR doesn't think Nate McLouth is a very good fielder. Personally, when I watched the Pirates this year and last, I saw in McLouth a fielder who didn't have the range many young centerfielders had, and one who consistently played too shallow, but I was surprised that his numbers were this bad. After all, he nicely handled most of the balls he did get to. But advanced fielding metrics pretty much universally reach the same conclusions about McLouth. Positioning may have something to do with it. But it's probably not some peculiarity that has to do with PNC's large outfield, or anything like that, since both Kenny Lofton and Tike Redman posted relatively good UZRs there.

So by replacing McLouth with Andrew McCutchen, who's blindingly fast (range is a very important part of outfield defense) and was universally regarded as a very talented defender as he came through the minors, the Pirates' outfield defense is likely to get even better. In fact, it isn't much of a stretch to hope they might have the best outfield defense in baseball for the next few years. This isn't just something to argue about over a beer; it's something that legitimate ly helps the Pirates win games.

Jason Bay and Nate McLouth were good players, and they'll be missed in Pittsburgh. Xavier Nady was a mediocrity, and I suppose he will also be missed in Pittsburgh. But in terms of the results, there's been no difference between the 2008 pre-trades Pirates and the 2009 Pirates. Some of that, again, is improvements in pitching, and the addition of productive players from the trades (Andy LaRoche, Ross Ohlendorf, and to a lesser extent Jeff Karstens) hasn't hurt either.

But perhaps the main reason the Pirates haven't gotten worse is that they've changed from a poor defensive team to a very good one, especially in the outfield. The fundamental complexion of the team is different. This isn't a change that's particularly easy for fans to see, which is one reason there continues to be lingering anger about the trades. The Pirates' old outfielders were active impediments to the Pirates' pitching staff, because they just didn't get the job done in the field. Now they have outfielders who do.

Forget about McLouth's Gold Glove; it's a ridiculous award. There are many better, faster centerfielders out there, and the Pirates have one in McCutchen. And so, while I wasn't thrilled about the return in the McLouth trade, don't be surprised if it doesn't actually sting much in the wins column, even in the short term. McCutchen won't hit as well as McLouth, but his defense will help the pitching look better.

That last paragraph could end up making me look ridiculous; of course it's possible the Pirates could play badly the rest of the year, especially if other players are traded. We've all seen enough Pirates baseball the past decade or so to know that predicting success, even on an extremely modest scale, is usually a very stupid thing to do. My point , though, is that the Nate McLouth deal, like the Bay and Nady deals before that, can't be e valuated simply by adding up a bunch of home run and RBI columns. It's a lot more complex than that.

The main point of the McLouth trade is to continue to rebuild. But by replacing McLouth with a much better fielder in McCutchen, and by adding Charlie Morton to the pitching staff at some point in the near future, the Bucs have set themselves up so that they might honestly expect to not play that much worse in the short term. They'll miss McLouth's bat, but they'll love McCutchen's glove. The Bay, Nady, and McLouth trades were made with the long term in mind, but the Pirates may not have to take much of a hit in the short term, at least not on the field.