Posted by Andy on November 12, 2010
Following up on my earlier post about HBP rates, let's take a look at the split in HBP rates by league...
As you can see, they have tracked fairly closely for most of the last 110 years. There are, however, some fairly significant differences. You can see that around 1910 and 1920, the AL hit batters at a noticeably higher rate in numerous seasons. The latter bump was probably due to Babe Ruth and others hitting a lot more homers, resulting in pitchers trying to push hitters off the plate.
But check out what happened in the 1970s, 80s, and 90s. The AL opened up a gap starting in the early 1970s that lasted until the mid-1990s.
The first thing that popped into my head was that this much be due to the DH. If AL pitchers didn't have to have their own turn at bat, then they might be more likely to plunk opposing hitters knowing that they didn't have to risk getting hit themselves. There we might expect to see AL HBP rates go up starting in 1973 (with the DH). Then, they might settle back down again starting in 1997, when interleague play started, meaning that AL pitchers had to hit again. True, they only had to hit a few times a year and only against certain NL teams, but perhaps they generally feared being plunked by any other team if they had a reputation as a plunker themselves.
Looking at the data more closely, though, this first instinct doesn't seem correct. The AL and NL rates actually diverged in 1967 and stayed apart (despite convergences in 1969 and 1982) until 1994, not 1997. So neither end of my initial theory seems to hold true, although it's possible that there are other fluctuations overlaid on top of a gap caused primarily by the DH. This is certainly possible, given the large differences we see at other years when there was no DH.
What else might be contributing? Here are some thoughts:
- The gap that occurs roughly during the DH & no interleague play era (1973-1994) could be due to DHs themselves hitting. In other words, when pitchers bat, then tend to get hit less since the opposing pitcher is not too concerned with moving him off the plate. He might get hit just due to natural wildness (which I assume is why most HBP occur) or in retaliation for a previous hit batter, but he's not going to get brushed back too much just due to his merits as a batter. If this were the case, we might expect to see about 12% more HBP in the AL vs. the NL (that's one additional batter over the 8 non-pitchers in an NL lineup) and indeed that's about what we see for much of the 1970s. But throughout the 1980s, there were about 30% more HBP in the AL.
- The HBP rates suddenly got a lot closer in 1993 and then crossed in 1994. This is probably due to the league-wide increase in offense that started in 1993. Pitchers probably started trying to move batters off the plate, thus increasing HBP. Whether the interleague play that started in 1995 had any affect is unknown, but it seems unlikely to be a big factor. It would seem to be unlikely to account for the complete elimination of the 12% increase in the AL we might have expected to the DH alone.
- When offense levels dropped in the late 1960s and into the 1970s, HBP levels dropped with them. This makes sense. It may be the DH that kept the AL rate from dropping as much as the NL rate. What's weird is the sharp increase in HBP rates from the mid 1980s to 2000. Offense went up, sure, but the HBP rates really skyrocketed during that period, topping out roughly around 2001 when offense itself spiked. HBP rates have fallen off since then as offense has fallen off. As a commenter said in my previous HBP post, this is probably because approach at the plate has changed, with most batters really crowding the plate, trying to take reach outside pitchers. Closer to the plate means more hit batters.
- I took a look at an Event Finder from the years 1976 to 1981, picked as a 6-year span with a big gap between the AL and NL in HBP. Overall, there were 4,122 in MLB over that period. Of those, 284 were DHs, all in the AL obviously, and 76 were pitchers, all in the NL (I checked.) If the rest of the HBP were split evenly between the leagues, that would be 1,881 per league, meaning the AL would have had an HBP "advantage" of 2,165 to 1,957. That would mean an average increase in the AL of about 10.6% vs. the NL. However, in reality, the AL led the NL by an average of 23.3% over that period. So it's not just the DH.
Hmm...what else is going on here?