By Jim Allen

At the conclusion of this year’s interleague play on Thursday, the Pacific League’s cumulative record against the Central League 1,040 to 920 since interleague was created in 2005 as a part of the settlement of Japan’s only players strike so far.

For a long time, most of us simply assumed the leagues were relatively even in terms of quality. But the lack of CL championships in the Japan Series and the typically one-sided interleague results suggests that in some way that the PL simply has more talent. I was pretty slow to accept this until Yakult Swallows pitcher Shohei Tateyama answered my question about why the PL did so well by saying, “Don’t you think it’s because they’re just better than we are?”

Looking at NPB interleague games from 2009 to 2017 played in NPB’S 12 main parks, Tateyama’s observation appears to be correct. The first thing everyone seems to point to is the pitching.

In February 2006, then-Nippon Ham Fighters manager Trey Hillman said it was tough for the PL teams because few PL pitchers threw really hard. Other than Australian Brad Thomas, Hillman said, his hardest thrower at the time was a pitcher who probably would be in Double-A in the U.S. (Yu Darvish), and that his hitters were not used to the velocity of the hard-throwing CL pitchers.

A year ago, Alex Ramirez said the opposite, that the PL pitchers–particularly the relievers–throw harder, and that makes it harder for the CL hitters to adjust. This appears to be the case at the moment. According to analysis site Delta Graphs PL fastballs are 0.6 KPH faster on average than the CL heaters, although the site doesn’t permit comparisons of starters and relievers.

The big problem with comparing the leagues is context. It doesn’t help just to look at raw numbers, because the two leagues’ parks, and the DH, affect run scoring differently. The biggest issue is perhaps the ballpark contexts. Until recently, the PL was dominated by huge parks with vast outfields and high walls, where home runs were scarce and speed was at more of a premium. That has changed in recent years with the switch in the CL from small Hiroshima Citizens’ Stadium to more spacious Mazda Stadium, and by the Hawks and Eagles both decreasing the home-run distances by adding field seats inside the outfield wall.

If one looks only at the same main stadiums, and how each home team fares against visitors in league and interleague play in the same part of the season, then perhaps one can get a clearer picture. NPB’s interleague used to run from the middle of May to the middle of June, and now occupies the first 2-1/2 weeks of June in its new 18-game format.

Most speculation has been that PL pitching is superior. If that is the sole cause, one would expect the CL pitchers to do as well against visiting PL hitters in interleague as they do against visiting CL batters in May and June. To study this, a data set was constructed of all non-pitcher plate appearances in the 12 main parks in May and June from 2009 — when Hiroshima’s Mazda Stadium opened — to 2017.

The data does not prove PL pitching staffs and defenses are superior but suggests that may be the case, but it also indicates that PL teams are better at hitting, playing defense and have superior speed in the outfield.

Pitching

PL home teams scored 3 percent more runs per 27 outs against visiting CL defenses in May and June than against PL visitors. In contrast, the CL teams score 9 percent fewer runs in their home parks against PL visitors than they do against their regular CL rivals. These findings are consistent with the idea that PL pitching is superior.

Batting

The data suggests PL offenses are also better than those in the CL. CL home teams allow 4 percent more runs per 27 outs when the visitor is from the PL, while PL pitching staffs have far less trouble with visiting CL teams than PL visitors in May and June, allowing 14 percent fewer runs per 27 outs.

Fielding

In terms of getting hits on balls in play, home offenses in both leagues do better against interleague opponents who rarely visit their parks. The PL home batters had an edge in this area, a 3 percent increase in interleague batting average on balls in play, while CL home offenses’ BABIPs improved by 1 percent against PL visitors.

There is, however, a huge difference in what goes on when the visiting team is at bat in interleague play.

Visiting PL teams in interleague batted .310 on balls in play against CL home defenses that held their own CL league opponents to a .296 average. PL home defenses, on the other hand, surrendered a .306 BABIP to PL teams, a .290 BABIP to visiting CL teams.

Strikeouts

Like visiting defenses, hitters also seem to have trouble in the unfamiliar parks of their interleague opponents striking out more and walking less.

It’s at home where the difference is obvious. At home in interleague, CL hitters’ strikeouts rose by 13 percent against visiting PL pitchers, while PL hitters’ Ks were 2 percent less frequent when a CL club was in town.

Built for speed

One comment often heard about the PL teams is that they’re faster — especially in the outfield, a necessity in a league with lots of large turf outfields.  PL home teams allow 8 percent fewer doubles and 8 percent fewer triples against CL visitors than against PL visitors. Central League home teams surrender triples 8 percent more often against PL teams than against CL opponents.

When PL teams host interleague games, their batters’ triples and doubles increase. When CL teams host, their doubles and triples decrease.

Although PL teams appear to have a speed edge in interleague, the one area where CL teams actually do better is in preventing stolen bases. Stolen bases percentages go down for visitors in interleague, with the PL being hit slightly harder. At home, CL teams actually improved their stolen base success rate, while PL interleague hosts were less successful stealing bases than they were in league play.