The AL Is Stomping the NL Again

I read a FiveThirtyEight article not too long ago from Michael Salfino, and it had the following headline:

Who Needs A DH? The NL Is Outhitting The AL, Somehow

Now, I’d never actually thought before to just look at league-by-league OPS. And, since that article was published, the point around which it was built has become untrue. Nevertheless, by OPS, the leagues are close. Courtesy of Baseball Reference, here’s how the leagues have compared over more than the past century:

I know that’s a little hectic, but right now, the AL has an OPS just four points higher than the NL OPS. Since 2000, on average, the AL has had the higher OPS by 14 points. Hey, it’s something. And it’s enough to make you wonder, is the NL finally closing the gap? Has the National League basically caught up to the American League, in talent and performance? There’s really only one good way for us to easily investigate, and it’s a little early to be conclusive. We’re barely a third of the way into the season and into interleague play. But based on the evidence to this point in 2017 — well, you saw the headline. The NL has gotten stomped. Surprise!

Every year, there are 300 interleague contests. At this writing, there have been 103 this season, and the AL has won 61 of those. That’s good for a .592 winning percentage — essentially the Yankees’ winning percentage — and here’s how things have gone since the concept was put into action roughly a couple decades ago:

The same fact remains the same fact. The last time the NL won the majority of the interleague games was in 2003. This would stand as the 14th consecutive year of AL supremacy, and although that winning percentage is obviously far from locked in, it would be the second-highest winning percentage we’ve observed. Back in 2006, the AL won 61% of the time. In 2008, the AL won 59% of the time. That’s happened again, as the AL has refused to allow the gap to shrink to nothing.

There are levels to be analyzed, of course. Always the usual levels. Has the AL just outplayed its own performance, or something? Here’s a similar plot, only this time showing Pythagorean winning percentage, which is based on run differential instead of, you know, wins:

That’s a little less noisy, but then, that’s what you’d expect. This year, the AL is still up at .565. That would be the sixth-highest AL Pythagorean winning percentage. And the last time the AL was outscored was in, well, 2003. This is the evidence to point to when people suggest that the NL suffers from some systemic interleague disadvantage. There was no meaningful, observable disadvantage over the first seven years. A gap has just developed, and the NL hasn’t been able to close it.

There’s one more area to look at, and it’s actually my favorite area to examine, with just a third of the games or so in the bank. Wins and losses can be noisy, but runs scored and allowed can also be noisy. This, therefore, is a simple plot of OPS differential, or NL OPS subtracted from AL OPS. This would closely mirror BaseRuns performance, and any positive result shows an AL advantage. To the data!

Right. The last time the NL had the higher OPS in interleague play was in 2002. That particular advantage was all of two points, or, if you prefer, two-thousandths of one point. Last year, the NL closed to within 12 points, but the gap has since widened to 52. If finalized, that would stand as the AL’s fifth-largest advantage in the 21 seasons, although as recently as 2015, it was a pinch higher. The point simply being: The AL is still better. If you believe, that is, the results of the games played between teams in each league.

One note about that. By the end of the season, everything should be more or less equivalent. Now, though, not all teams have played the same number of interleague games. Here is the landscape of AL participation:

Meanwhile, here’s the NL picture:

Something probably stands out there. The Dodgers are the only team that has yet to participate in interleague play. And the Dodgers are good! Their so far being absent would stand to make the NL look worse than it is. But that’s making too much of the influence of one ballclub. After running the math, the AL teams have averaged a weighted .497 winning percentage against other AL opponents. The NL teams have averaged a weighted .501 winning percentage against other NL opponents. The scales, then, haven’t overall been tipped. Each league has faced roughly equivalent strengths, Dodgers be damned, and the NL has lost a whole bunch.

This isn’t anything shocking. This probably doesn’t even count as anything interesting, not now, not after so many years of writing the same articles. I think we all assumed the AL would remain the superior league, for many of the same reasons as always. How to explain how the NL is close to the AL in overall league OPS? That’s probably as simple as asserting that the pitching in the NL is weak. So it inflates the hitting numbers, which subsequently suffer when they face tough interleague opponents. Pitching might be the NL’s greater weakness, and it’s not a coincidence the NL is where the majority of the rebuilding ballclubs are found. Eventually, the NL will be better. They’ll have an advantage in talent, if not in resources.

They just haven’t had that advantage for a while. And it sure doesn’t seem like they have that advantage in 2017. There’s plenty of interleague baseball still to go. There are plenty of interleague baseball updates still to be written. If I had to guess, you probably won’t need to read them, because you’ll probably be able to guess what they say.