Read Part 1.

Five things I learned about fielding in baseball from reading Bill James’s new book Win Shares:

1. Defensive efficiency, the percentage of balls put into play that is turned into outs, defined, if we ignore the small peripherals, as total outs minus strikeouts divided by the total number of balls in play, accurately measures how well a team performs defensively. You might think that pitchers would influence this statistic. They don’t.

2. You can measure range for first basemen, but this requires not just assists, but unassisted putouts, which are usually made when he runs to the bag himself instead of flipping to the pitcher. You can approximate this second component by subtracting all of the other infielders’ assists from the first baseman’s total putouts.

3. Catcher fielding percentages are a lot more meaningful when you remove strikeouts, which absurdly bloat the catcher’s total chances and never should have been there in the first place.

4. Because fielding, unlike pitching or hitting, is a cooperative effort, it must be evaluated top down — first on the team level, and only then by assigning contributions to individuals. (James also argues that this is the best way to evaluate *everything*, but I’m sure he would agree that you can get a lot further with pitching and hitting by working from the bottom up.)

5. Fielding statistics, like many things, make a lot more sense in context. If Bill Mazeroski, who has the best all-time double play statistics of any second baseman, turned a lot of double plays, we need to figure out how many he had a chance to turn, and we can. If Richie Ashburn, who has the best all-time fielding statistics of any outfielder, caught a lot of fly balls, we need to figure out how many he had a chance to catch, and we can again. In fact Ashburn achieved them partly because he was in fact a superb defensive player, but mostly because the Phillies’ pitching staff in the 1950s gave up more fly balls than any other pitching staff ever, by far. For the same reason that team’s shortstop, Granny Hamner, has lousy fielding statistics, even though his defensive reputation was excellent. Mazeroski, on the other hand, had more or less the normal number of opportunities to turn double plays. He really was that good.

Maybe these things are obvious. But I didn’t think of them, and neither did you.

The claim that pitchers dont affect batting average on balls in play is only a couple years old–and James wasnt the one who did the study that first showed it, though I forget the guy’s name–and it’s still a bit controversial and incomplete.

This is my understanding of the current state of the matter: First, the claim is not that pitchers dont affect this but that they influence is rather slightly, though it does seem that knuckleballers as a group do reduce batting average on balls in play. The evidence for this is the wild variation from one year to the next in this statistic for any given pitcher, although the career graph for good pitchers seems to be more impressive on this score than for bad pitchers. And the variation from year to year is so great that more than defense–which is after all usually provided by the same guys in any 2 consecutive years–has to be invoked to account for it: i,e, luck.

But, if this is true, how do you explain of often great disparities in this statistic for pitchers on any given team, all playing in front of the same defense? (It could be that the balls in play allowed by each pitcher test the defense differently, depending on whether they’re groundballers or flyballers or righty or lefty. But on one has studied this.)

The other thing is, nobody has studied whether slugging percentages on balls in play is greatly affected by the pitcher. I suspect it is, but I wish the guys with the data and software would study this. It seems important.

The guy’s name is Voros McCracken, and his site is here. McCracken answers most of your questions better than I could, but briefly:

It’s true that knuckleballers have a lower batting average against than other pitchers. But the difference is small, on the order of 5 or 10 points. The variation between pitchers on the same staff, in front of the same defense, can be explained the same way year-to-year disparities between the same pitcher can: by luck. If the variation was meaningful then the same pitchers would give up fewer hits every year. Doesn’t happen.

Everyone agrees that pitchers affect slugging percentage. Slugging against data is unfortunately spotty (I don’t have it, for instance), but some guys consistently give up a lot more home runs than other guys, and homers plus batting average is an excellent proxy for slugging.