Comparing NPB’s slap-happy 2010s with the old days

A while back, I wrote about the NPB ballpark experience of the early 1970s. It seems hard to imagine in Japan’s relatively polite society today, but violence on the field and in the stands was something you saw if you went to the ballpark.

Those anecdotes came out of searching through newspaper stories to understand the context in which the Hiroshima Carp won their first pennant in 1975, and in a sense I was looking for the data set that I am only now just getting my hands on.

Having recently compiled the play-by-play data from some old seasons, 1958 through 1963, 1969 to 1970 and 1999 to the present, I was curious how the left- and right-handed-hitting populations in NPB looked in another era.

Previous posts on this topic can be found here from oldest to newest:

• Does NPB type caste?
• Japan’s left-side story
• NPB left in the lurch
• Let’s get small
• Then and now

The measures: or who you calling a ‘slap hitter,’ bud?

In the last post, I looked how three groups of domestic hitters who were not pitchers performed when having the platoon advantage. The essential definition is whether a hitter is a “slap hitter” — a player who is basically a singles hitter — or not.

To measure this, I looked at every 300-plus plate-appearance season in NPB since 1950, excluding those of foreign hitters. Each player was compared to the averages of that group of domestic hitters in that season in the percentage of his hits that were doubles and home runs. Each players averages for home runs and double were then rated by how many standard deviations they were above or below that year’s mean for domestic regulars.

Each player since 1950 had his variance from his 300-plus PA seasons averaged. Players whose career average in the frequency of doubles of home runs and doubles was more than a half a standard deviation below the mean were classified as slap hitters. All other players with at least one 300-plus PA season were classified as “Non-slap hitters.” This allowed for a third group, players who have not had 300 plate appearances in a season and are thus unclassified.

To eliminate the platoon edge that left-handed batters get from facing right-handed pitching much more often, I have compared each group only with the platoon advantage. Thanks again to Tom Tango for that tip.

Some basic observations about the data

Left-handed slap hitters in Japan ground out A LOT, with 59.7 percent of their outs in play hit on the ground since 2011. They were the outliers in ’69 and ’70 as well, with 57 percent of those outs on the ground.

When making ground outs, left-handed hitters as a class are less likely to hit to the pull side of the infield. This was true in 1969-1970 and it’s true today.

Left-handed slap hitters are thus, according to the Jinji hypothesis (see the last post), the kings of infield singles. In 1969 and 1970, 18 percent of their singles never left the infield, the best figure among hitters with the platoon advantage in NPB. Since 2011, that figure has been 18.6 percent while the rest of the hitting populations — likely in response to the introduction of artificial turf, have seen a smaller share of infield hits.

When it comes to hitting for extra-base hits, the less power a batter has, the more likely he is to get his few extra-base hits to the pull field, which makes perfect sense. Singles into the outfield work the other way with slap hitters getting fewer singles to the pull field than other batters.

Actually, 1969 and 1970 are poor years to study the matter, since that time marked the end of a period starting around 1966, when the proportion of slap hitters was about the same among left- and right-handed batters. Throughout most of NPB history, it appears that lefties were more likely to be punchless wonders.

Other than the overall decrease in infield singles, then what other semi-trends raise their heads from these two data sets?

Batters drive the ball much more to center and the opposite field than they did 50 years ago.

HRs by LHB since 2011 with platoon advantage

HRs by RHB since 2011 with platoon advantage

HRs by LHB in 1969-1970 with platoon advantage

And to help visualize this trend better, if it is a trend and not just a small-sample error. Here is the overall field distributions for HRs in the two periods we’re looking at.

HR distribution with platoon advantage