Lies, Damned Lies: Trying to Get LOESS-t

In playing around with the McCain-Obama polling data over at my political blogging project, I came across a procedure known as a LOESS regression. LOESS is a way to create smooth-looking curves out of sequential data. Some of LOESS’s virtues are aesthetic; the curves it produces seem to look and feel just right. But it can also be considerably more robust than something like a moving average in handling time series data, performing more strongly in the presence of outliers. Since we look at all sorts of time-series data in baseball, LOESS ought potentially to have all kinds applications to the game.

Today I am going to start with a simple application: how the eight primary fielding positions have progressed since the 1950s. The metric I am using is the OPS accumulated by all players at a given position each season relative to that of the league as a whole. I don’t include pitchers or designated hitters in the league-wide averages, as offense at the former position is mainly a fun little curiosity, whereas the latter would skew the results, as the DH position was created solely for offense. (Ironically, designated hitters as a group have quite frequently been outhit by both corner outfielders and first basemen.)

Let’s begin behind the plate:

Rest assured, the other graphs are a little bit more interesting than this one, but it says something that the catcher position has had roughly the same strength for the past 50 years. At every other position, teams can consider shifting their personnel around to strike the offense-defense balance that is fashionable in their day. But a catcher is just a catcher (unless he’s Craig Biggio), and the sort of John Russell / Josh Willingham / Robert Fick experiments have never really caught on.

First base is another relatively stable position, but there was a bit of a miniature Golden Era in the mid- to late ’90s, when guys like Mark McGwire, Todd Helton, Jeff Bagwell and Rafael Palmeiro were all in their peaks. We are in a relatively down period for first base talent now, but as you will see, it is not unique among the corner positions in that regard.

This is not something I was really aware of beforehand, but second base has steadily become more and more of an offensive position over the past half-century. During the neo-Deadball Era of the mid-’60s, and particularly before the pitchers’ mound was lowered, baseball was very groundball-oriented, and so it made sense to have two premium defenders in the middle infield. Even since then, however, the position has tended to gravitate toward offense. In certain ways, second base has become a bit of a rover position, full of guys with weird, disparate skill sets-like Luis Castillo, Rickie Weeks, Dustin Pedroia-who don’t quite fit in elsewhere on the diamond but who nevertheless can be fairly valuable.

It’s pretty widely known that offense at the third base position has been booming, to the extent that it now makes more sense than ever to group the “four corner” positions together. Whether this is the result of a few preternaturally talented players like David Wright or some shift in philosophy, I’m not certain, but third base talent has always seemed to come in waves, with the last peak right around 1980, when George Brett and Mike Schmidt were in their heyday.

Although the inflection point on this graph comes during the early 1970s-that was a few years after Ray Oyler had hit .135 for a World Series winner-what’s surprising is that shortstop play has continued to get better and better even with the Trinity having come and gone. It might just have been a matter of teams looking at Alex Rodriguez and recognizing that they could have their cake and eat it too. Another factor is the increasing number of Latin American players in the game, who tend to be concentrated in the middle infield. Shortstops are having a bit of a rough year so far in 2008, however.

We are really in something of a lull for outfield talent; the way I discovered this was by playing in a roto league that requires you to field six outfielders. You can really see the impact of Barry Bonds‘ numbers on this position, by the way; he shifts the whole shape of the LOESS curve all by himself.

There was a time back in 1950s when left fielders were performing discernibly better than right fielders-and left field is considered the easier position on the Bill James defensive spectrum-but ever since then, the two corner outfield slots have tracked extremely closely. That’s only fitting, because the transaction costs of moving a guy from left field to right are virtually nil. Once again, however, we see the position in some decline. Might it be that teams are starting to place more emphasis on corner outfield defense? I would guess that advanced defensive metrics are more marginally useful to teams in their evaluations of outfielders than of infielders, as outfield defense tends to be a little bit harder to eyeball.

The most dramatic shift has come at center field, which has gone from being an above-average offensive position to one that’s distinctly below average. Granted, we are starting our graph right in the era of Willie, Mickey, and Duke, but the decline of center field offense has been steady over the past 50 years. My pet theory is that this might have to do with the decreasing participation of black players in the game; among the top 50 seasons for VORP at the center field position since 1957, 27 were accomplished by African-Americans.

Finally, we can look at everybody together, with the individual data points stripped out and just the LOESS curves remaining. In just the past few seasons,we have seen catcher overtake shortstop as the least productive offensive position. For a long while, in fact, catcher was ahead of second base. In many ways, the talent distribution more closely follows Bill James’ defensive spectrum now than when James created it back in the 1980s. At that time you could have had a real argument about whether third base or center field was a more important position, and you might have had trouble proving the proposition that catcher is more difficult than shortstop. The former is no longer a viable argument, however, while the latter finally squares with the evidence.