Posted by Andy on December 27, 2010
We chatted about intentional walk rates on a recent thread, so I thought I'd look into the numbers a bit more.
What I've found is that the National League has always had more intentional walks than the American League, even before the advent of the designated hitter.
Click through for more.
Here is a plot of the average number of intentional walks per game (that's per team, not total for both teams in a given game) each year, broken down by league.
As you can see, there has always been a large gap between leagues, although that gap got bigger in 1973 when the DH came around.
We can break this down into three eras:
- From 1955 to 1972, the NL averaged about 0.09 IBBs per game more than the AL. That's about one every 11 games--certainly not a huge difference, but a fairly consistent one.
- In 1973, the difference soared to 0.19 IBBs per game, nearly 1 every 5 games on average, and from 1973 to 1990 the average difference was 0.16 IBBS per NL game (one every 6 games or so.)
- From 1991 to 2010, the difference reverted back to about 0.08 IBBs per game, or about 1 IBB per 13 games.
Although these differences are pretty small--would any casual observer notice an extra intentional walk every 13 games?--they are quite consistent over the years.
My big question is--why? It's clear why there would be more intentional walks in a game where pitchers hit. In particular, the 8th-place hitter would get more intentional walks in order to bring up the weak-hitting pitcher. But the differences go beyond just the designated hitter effect.
Here's a little bit of data about IBBs in 2010.
For the 1,216 intentional walks, they broke down by batting order position as follows:
Predictably, 8th-place hitters got the most, while 9th-place hitters got the fewest. (The 9th place hitter almost never intentionally walks in the NL.) The 1st place hitter doesn't get many either, in particular because he's never walked leading off the first inning, the the 2nd-place hitter who usually bats right before his team's best hitter (the #3) is rarely intentionally walked either.
Of the 232 IBBs to 8th-place hitters, I counted only 34 that were issued by AL teams, and of those 12 came in interleague games in NL parks (when the DH rule was not in use.)
Still, this difference doesn't account for the entire difference between leagues....what other factors haven't I mentioned?