A Japan Baseball Weekly Podcast listener (@DarkMatter89) who spends time tracking the distances of home runs hit in Nippon Professional Baseball, suggested that last year’s home run increase (12.1 percent over 2017) has continued into 2019.
Let’s compare the data each year through April 29.
| Year | PA | HR | HR rate | Change |
| 2010 | 13571 | 292 | 0.022 | |
| 2011 | 6227 | 112 | 0.018 | 0.818 |
| 2012 | 10248 | 100 | 0.01 | 0.556 |
| 2013 | 12151 | 215 | 0.018 | 1.8 |
| 2014 | 12055 | 258 | 0.021 | 1.167 |
| 2015 | 11780 | 160 | 0.014 | 0.667 |
| 2016 | 12505 | 219 | 0.018 | 1.286 |
| 2017 | 10723 | 186 | 0.017 | 0.944 |
| 2018 | 10727 | 228 | 0.021 | 1.235 |
| 2019 | 11873 | 320 | 0.027 | 1.286 |
As many of you know, until 2011, NPB had no standard ball, but allowed clubs to use balls from up to three different approved sporting goods makers during the season, provided they used each ball in at least a third of their home games.
In 2011, a uniform NPB ball was put in play with the target coefficient of restitution set near the absolute minimum allowed by the rules. As a result the ball was very dead. The 2011 season was a terrible year for home runs, with the frequency per PA dropping nearly 40 percent.
That wasn’t readily apparent at the start of the season, for reasons related to the Great East Japan Earthquake of March 11, 2011. Two Pacific League stadiums were unready for Opening Day. The Rakuten Eagles’ home park and its facilities were earthquake damaged, while the Lotte Marines’ park suffered from a lack of running water because water mains in the reclaimed areas along Chiba Prefecture’s Tokyo bayside had ruptured.
As a result of that, the season started two weeks late, missing some of the season’s coldest early weather. Because of the meltdowns at the Fukushima No. 1 nuclear power plant, ballparks in the eastern part of Japan’s main island of Honshu were prohibited from playing night games in April. As a result, there were day games or home games played in smaller regional parks in western Japan. Until the second half of the season, parks in the areas affected by the electric power shortage were also required to use reduced lighting.
Because of those influences, the dead ball apocalypse was slow in revealing itself. Because the season started late, it also ended late with league play going until Oct. 25, making the overall home run figures worse than had the season gone from March to early October.
In 2013, a coup d’tat overthrew commissioner Ryozo Kato, who had introduced NPB’s first standard ball. It was started by a senior official, who is now in charge of NPB’s bureaucracy, in a conspiracy with ball manufacturer Mizuno, which had long catered to the wishes of the teams to produce baseballs that were exceedingly lively.
But the overall growth in home run figures are not exclusively related to the ball. After the 2014 season, the owner of the SoftBank Hawks recalled the club’s lively-ball power-rich past and ordered the fences brought in to facilitate that. Since then, the Eagles and Marines have both followed suit.
Lumping together two-year periods to lessen the effect of weather, home runs in the CL in 2018-2019 increased by 18.5 percent over 2016-2017. The PL during the same period is 27.7 percent.
So let’s turn to 2019 and look for park-by-park increases over 2018.
Main Park HRs through 4/27/2018
| Team | PA | HR | HR PA |
| Giants | 690 | 20 | 0.029 |
| Tigers | 681 | 6 | 0.009 |
| Dragons | 813 | 7 | 0.009 |
| BayStars | 869 | 15 | 0.017 |
| Carp | 615 | 16 | 0.026 |
| Swallows | 623 | 20 | 0.032 |
| Buffaloes | 468 | 5 | 0.011 |
| Hawks | 805 | 28 | 0.035 |
| Fighters | 676 | 14 | 0.021 |
| Marines | 696 | 8 | 0.011 |
| Lions | 673 | 16 | 0.024 |
| Eagles | 1043 | 18 | 0.017 |
| Team | PA | HR | HR PA | Increase |
| Giants | 543 | 26 | 0.048 | 1.652 |
| Tigers | 687 | 18 | 0.026 | 2.974 |
| Dragons | 797 | 14 | 0.018 | 2.04 |
| BayStars | 881 | 22 | 0.025 | 1.447 |
| Carp | 1160 | 24 | 0.021 | 0.795 |
| Swallows | 966 | 38 | 0.039 | 1.225 |
| Buffaloes | 701 | 15 | 0.021 | 2.003 |
| Hawks | 779 | 29 | 0.037 | 1.07 |
| Fighters | 782 | 13 | 0.017 | 0.803 |
| Marines | 986 | 31 | 0.031 | 2.735 |
| Lions | 791 | 21 | 0.027 | 1.117 |
| Eagles | 907 | 23 | 0.025 | 1.469 |
As I may have mentioned on the podcast, the Tigers had an absurdly low number of home runs at home last season, and this looks partly like a regression. Throw out Chiba, which changed this year, and you still get nine out of the 11 clubs seeing more home runs in their main parks.
Last year about this time, I reported that home runs were increasing much more than the increase in balls hit in the air, which showed a slight growth in 2018. So far this year, however, fly balls appear to be down, while strikeouts are following America’s model and still on the rise.
