Some of you might have been too distracted by recent events in Israel and Iraq to notice the most important event of the summer: the publishing of the results of a major study by Diamond Mind Baseball testing the veracity of the radical “DIPS” theory of Voros McCracken. For those who might be unaware, McCracken’s theory is that pitchers have little if any impact on the outcome of balls put into play; whatever happens to balls put into play is attributable to the defense or luck. Most tests of McCracken’s theory have tended to support it; it has been endorsed by Bill James and made famous by Michael Lewis in Moneyball.
Well, the people at Diamond Mind did an exhaustive study of the previous 90 seasons to test McCracken’s theory. And the punch line was:

I am convinced that pitchers do influence in-play outcomes to a significant degree. There's a reason why Charlie Hough and Jamie Moyer and Phil Niekro and Tom Glavine and Bud Black have had successful careers despite mediocre strikeout rates. There's a reason why the top strikeout pitchers have also suppressed in-play hits at a good rate. Using power or control or deception or a knuckleball, pitchers can keep hitters off balance and induce more than their share of routine grounders, popups, and lazy fly balls.

Those results are noteworthy enough, but the ramifications are greater than I’ve seen discussed anywhere on the Net.
Aside from McCracken’s theory, the greatest advances in sabermetrics over the last couple of years have been in measuring defensive performance. The most noteworthy examples are the the defensive component of Bill James’ “Win Shares” and similar methods used by Baseball Prospectus.
At the heart of both of those methods are analyses of the outcomes of balls put into play against the defense. They thus were developed in partial response to the issue that Baseball Prospectus called one of the game’s “Hibert Problems” in its 2000 book – namely, how to distinguish the respective contributions of pitching and defense to run prevention. Or, as Michael Lewis writes on pp.235-236 of Moneyball:

…Voros saw someone say that no matter how much research was done, no one would be able to distinguish pitching from defense. That is, no one would be able to distinguish pitching from defense. That is, no one would ever come up with good fielding statistics or, therefore, good pitching statistics. If you don’t know how to credit the fielder for what happens after a ball gets put into play, you also, by definition, don’t know how to debit the pitcher. And, therefore, you would never be able to say with any real certainty how good any given pitcher was. Or, for that matter, any given fielder.
When Voros read that, “I thought, ‘That’s a stupid attitude. Can’t you do something?’…”

And he began the research that would culminate in his “DIPS” theory.
Here’s the problem: As noted above, the new advances in the measurement of fielding performance are based on analyses of the results of balls put in play. As such, absent McCracken’s theory, they are based on a kind of question-begging: they assume that the results of balls put into play are attributable to the fielders rather than the pitchers. If the pitchers influence the results of balls put into play, then don’t you have to take that into account? And if that’s the case, then haven’t you merely reopened the “Hibert Problem” of distinguishing pitching and defense?
McCracken’s theory had value beyond what it said about pitchers’ performance. By largely removing the influence of pitchers from the results of balls put into play, it also provided the justification for the foundation of Bill James’ and Baseball Prospectus’ methods of measuring fielding performance. But now, it seems like we have taken several steps backward. To use an example cited in the Diamond Mind study, in measuring the defensive performance of the Seattle Mariners over the last several years, don’t you have to adjust for the influence of Jamie Moyer? And again, doesn’t that merely reopen the “Hibert Problem” of distinguishing pitching from defense?
Maybe I’m missing something here, but I’m not sure what it is.
UPDATE: David Pinto supplies what I'm missing:

What Tippett is saying here is that you can predict strikeout rates pretty well just by looking at the previous season of the pitcher, but you can't predict -play batting average relative to the team well at all. That's what correlation means. Correlation goes on a scale of -1 to 1, where 1 is perfect correlation (the best at one will be the best at the other), -1 is perfect opposite correlation (the best at one will be the worst at the other) and 0 means no correlation at all; in other words, being the best at one will tell us nothing about how you do at the other. The statistican I learned from used to tell me that if he sees .5 correlation, he assumes the data is random. Seeing a .09 correlation tells me the data is very random. It's not 0, but it's very close to 0.
So, as to Dr. Manhattan's question; yes, you are missing something. The effect Tippett is showing is small, so small that DIPS is still valid. Bill James knew about this when he wrote win shares, but for the aggregate I think it works really well. We don't have to reopen the “Hibert Problem”; we just have to understand that the solution is just an approximation.

So what I was, and am, missing is a real education in statistics. Oh well...

ANOTHER UPDATE: I've just fixed my post. Sorry - my Baseball Prospectus 2000 is in storage so I couldn't double-check it. The correct term is "Hibert" problems. Those problems were a list of 23 fundamental mathematical problems propounded around the turn of the century by a mathemetician nmaed Hibert. In BP2K, Keith Woolner tried his hand at setting out a list of parallel questions, and a primary one was the distinction of pitching and defense. The piece helped inspire Voros McCracken.
A FINAL UPDATE: The name is "Hilbert," not "Hibert." Thanks to Mike Molloy for the tip.