The Seattle Mariners played the New York Mets on July 29 in a game I wish I'd paid closer attention to.
National League teams entered the day with a rare opportunity: With a 102-103 record in interleague play up to that point in the season, they could have pulled equal with their American League counterparts. But regardless of that day's outcome, something interesting seemed to be happening: After more than a decade of AL dominance in interleague play -- which, presumably, is the best measure of relative league strength -- this year's interleague play was actually balanced. The NL had finally, finally closed the gap.
It didn't happen that day, though. Yovani Gallardo, pitching for the AL's Mariners, struck out two and walked as many, but managed to outduel Jacob deGrom, who punched out 10 and walked one in a loss for the NL's Mets. The Mariners won the next day, too. Then the A's beat the Giants on July 31, and the dream was soon dead. Since July 29, the American League has gone 51-34 in interleague play. Balance was an illusion. The AL outscored the NL by 110 runs in those 85 games, hit .270 while the NL hit .240, outhomered the NL 110 to 84, and posted a 3.50 ERA to the NL's 4.88. And we're back to where we've been for 13 consecutive seasons:
In the first eight years of interleague play, the two leagues were mostly balanced. Since the beginning of the 2005 season, though, the American League has won 54.9 percent of interleague games. Its run differential is consistent with that dominance. The National League stinks.
There's a view that holds that the NL doesn't stink, but is just disadvantaged by DH rules. This view argues that AL teams have real DHs, while NL teams have to throw some bench bat into that spot for AL games, and that the gap there is bigger than the gap between NL pitchers and AL pitchers batting in NL parks.
This is wrong. What's actually happening is, as I said, that the NL stinks. I can show my work.
If we exclude DHs and pitchers and look just at each team's eight position players, the AL has easily outhit the NL in interleague play. Since 2010:
AL position players vs. NL pitchers: .265/.329/.424
NL position players vs. AL pitchers: .256/.317/.407
Relative to the AL, NL batters hit worse in the same games with the same rules. Simple.
Then, if we stick with those same groups of players -- designated hitters and pitchers still excluded -- we'll see the NL hitters' numbers go up when they're facing NL pitchers, and AL hitters' numbers go down when they're facing AL pitchers:
AL position players vs. AL pitchers: .257/.320/.409
NL position players vs. NL pitchers: .262/.330/.417
Relative to the AL, NL pitchers allow a bunch more offense.
Now, it is true the DH rule slightly favors the AL, but only slightly. AL designated hitters really do outhit NL designated hitters in interleague play. NL pitchers, as it turns out, outhit AL pitchers by almost exactly the same margin, but pitchers bat fewer times than DHs, so the AL does get some benefit in the tradeoff.
The DH league has won 58.2 percent of interleague games played at home (with the DH) from 2010 to 2017, but 49.5 percent of interleague games played on the road. Home-field advantage in baseball is pretty reliable, though - in that time frame, home teams have won 53.7 percent of all games. So the AL has won an extra 4.5 home games per 100, but also 3.2 extra road games per 100.
The AL's dominance is broad and convincing. NL pitchers in interleague play allow more home runs and strike out fewer batters, sure, but they also throw more wild pitches. They also allow more stolen bases. They also let more runners reach base on errors. They also commit more balks, for goodness' sake. They're just worse. The league is much worse.
There's actually a simple explanation: The AL spends a lot more money on players. The average Opening Day payroll in the American League this year was $145 million; the average NL payroll was $130 million. The AL collectively spent $233 million more on players than the NL. It might reasonably follow that if NL teams are thriftier in player acquisition, they might also be thriftier in aspects of team building: player development, front-office staffing, international scouting and so on.
So let's fast-forward to the World Series. We don't know who'll be there, but I'm confident predicting an NL team vs. an AL team. Do we do something with this knowledge?
Logically, the answer should be yes. What we think we know about these teams is skewed by the competition they've faced. If we think the Dodgers' .640 winning percentage and the Indians' .620 winning percentage are totally representative of their true talent, then the Dodgers should be favored 52-48 to win any single game (ignoring home-field advantage) against Cleveland. But the Dodgers have a .640 winning percentage against a league that stinks! And the Indians have a .620 winning percentage against a league that crushes the NL. A .500 team in the National League would win only 76 games in the AL; a .500 team in the American League would win 86 in the NL.
The Dodgers, then, wouldn't be a 104-win team in the American League. Logically, they'd be more like a 99-win team. (An explanation of how we calculated that is here.) Adjusting the rest of our likely playoff teams in the event of a league switch:
Anyway, that's the logical thing to do. In actual fact, the NL -- which stinks -- has miraculously held its own in the World Series during this stretch. The NL has scored slightly more World Series runs, won slightly more World Series games and held two more World Series parades than the AL since the start of the 2005 season. That's in only 65 games -- the much larger body of evidence overwhelmingly says the NL stinks. The AL's interleague dominance should matter in the World Series, but it hasn't. Baseball is weird, sometimes in ways that contradict its own weirdness.