[Outback Frito Pendejo]

I've been reading about this analysis that claims that MLB pitchers all tend to regress to a mean of around .290, so the only real difference between good and bad pitchers is home runs, walks, and strikeouts. Batting Average of Balls in Play supposedly is only influenced by luck and defense. This seems counterintuitive. An overmatched hitter who manages to get a little contact may get a lucky hit, but seems more likely to hit a weak groundball or a popup. Pitchers who make a lot of mistakes or have very hittable stuff sometimes get rescued by good fielding, but they also tend to have a lot of line drives yielding extra base hits.

[Grover]

I know you posted this a while ago, but baseball is back and it's time to get my sabre on....

BABIP is a pretty solid stat. Meaning that it's a fairly good indicator if a pitcher has been lucky or unlucky or blessed with good D or not.

.290 isn't a be all, end all. However, it does indicate more of the overall situation then just your standard stats.

For example, if you have a pitcher with good K and BB numbers, yet his ERA doesn't really seem to line up with that...think of Jeremy Bonderman . Good K and BB totals, but his ERA has always kind of sucked. His lifetime BABIP is .312.

Greg Maddux - .286
Roger Clemens - .286
Randy Johnson - .294
Chen-Ming Wang - .289
Eric Plunk - .286
Paul Byrd - .287

Now, there are definitely exceptions to the rule (El Duque jumps to mind, I believe his lifetime BABIP is like .270 or something), but there are an awful lot of pitchers across all talent levels that are in the .285-.295 range.

The main thing, though, is that the .290 number has come over looking at literally thousands and thousands of plays. HUGE sample size, so the number is pretty rock solid. Again, it's not everything, but when you look at it combined with something like HR/F (HR per fly ball) and GB% it can give a really good picture of if a player has been screwed a little bit by (or benefited from) the play of his team mates and/or lady luck.

[Outback Frito Pendejo]

Would slugging percentage per balls in play be less influenced by luck or defense? A good sinkerball pitcher might give up some seeing-eye singles, but doubles and triples would more likely reflect failure on the pitcher's part. Perhaps I'm just influenced by a lifetime of hearing that some pitchers can induce outs better than others.

[Confident Lefty]

Moneyball discussed BABIP a little bit and how pitchers have little control over it. In that part of the book, the author brought up Chad Bradford and explained that the A's coveted him because, as you said, he was a groundball pitcher, and ground balls are hard to hit for extra bases. He never mentioned slugging percentage explicitly, but that was basically his subject.

I was surprised by Pedro Martinez's BABIP stats for his two awesome seasons ('99 and '00). In 1999, he was 23-4 with a 2.07 ERA and 243 ERA+, but he did this with a .325 BABIP. In 2000, he was 18-6 with a 1.74 ERA and 291 ERA+, but his BABIP was a mere .237. While it may generally stay the same for most pitchers, his numbers in these two seasons were wildly different.