The American League Is Rolling Again

Let’s see, what are some of the current baseball headlines? With the Mets, Yoenis Cespedes is performing like an MVP candidate (for crazy people). Johnny Cueto’s season has taken a nasty turn in Kansas City. J.A. Happ has been a wonderful surprise find for the Pirates. Troy Tulowitzki might not play for the Blue Jays for a little while, but even the healthy version was offensively under-performing. Carlos Gomez hasn’t quite looked like himself. Cole Hamels hasn’t quite looked like himself. Maybe these aren’t all the biggest headlines in baseball, but they are at least things that are happening.

And there’s something all those players have in common: they’ve all very recently switched leagues. Some went AL to NL, some went NL to AL, and while the league switches don’t explain everything, you have to think they’re some kind of factor. In that, they can’t be considered irrelevant. Because, once again, the evidence points to the American League being the superior league. This isn’t anything new. Rather, this just continues a trend, a trend that’s lasted for more than a decade.

This is something I like to look at late every summer, and though this season isn’t yet totally complete, it’s most of the way there, and I’m an impatient person. The numbers we have now shouldn’t change very much. I want to take this chance to point to this recent Community post by Rob Mains — Mains did good work, and he pointed to the AL’s continuing superiority. Below, I’d like to show you more data, deeper data, so you can see how the numbers have bounced around.

There is no perfect way to compare the two leagues. As far as I can tell, there are three options:

1. make up stats
2. analyze the performances of those who’ve switched leagues
3. look at the head-to-head matchups

The first option is appealing, but dangerous. The second is interesting, but a little complicated, and limited by sample sizes. The third is the obvious one. Every year, the AL plays the NL a few hundred times, and while it would be analytically preferable if they played a few thousand times, there’s neither time nor demand for that much baseball. So we go with what we’re given, and we assume that a lot of the scheduling imbalances even out.

As I write this, there have been 281 AL-NL games. The last few years, they’ve ended up at 300. Previous to that, they settled at 252. Here’s a plot of American League winning percentage over time, in those interleague games:

The mark this year is .548, up from last year’s .543. The average over the whole span is .526. Overall, the AL has controlled interleague play, and it hasn’t lost at least half the time since 2003. This year has allowed the AL to further distance itself from the relatively mediocre 2013. But, say, you might be thinking that this is based on a somewhat small sample of games. Not that there’s much we can do about that, but what if we tried to erase some of the noise by looking at Pythagorean winning percentage? After all, run differential is important. Wins can be fluky.

Stronger. This year, the AL comes out at .569, compared to last year’s .540. The overall average is .532. This year’s Pythagorean record is the AL’s best since 2008, when the leagues were in a particularly lopsided cycle. Now I have just one more graph. The first was of raw wins. The second tried to strip away some noise. This one tries to strip away more. This eliminates sequencing, functioning a little like BaseRuns. Interleague OPS differential, from the AL’s perspective:

At +.056, the AL is again doing its best since 2008. The overall average is +.026, and only three times has the AL come up negative, the last time being 2002, when it was at -.002. This year suggests the AL might be getting back to its relative heyday, after some lower years. Or, it’s just a blip. These things are cyclical, but I can’t predict the cycle from here. I don’t see any reason to think the AL will give up this advantage soon.

Whenever this comes up, it’s always controversial. Sometimes NL fans feel disrespected, and, though there’s no fixing that, this is just what the numbers say. I assure you, I’d be delighted to write a similar post about how the NL has gotten stronger than the AL, were that to happen. I’m just writing what I see. Additionally, NL fans sometimes talk about how interleague play puts them at a disadvantage, because the AL has regular designated hitters. It’s not a clear-cut case, but even if it is somewhat true, the fact of the matter is that this year the AL is doing better against the NL than it has on average. So even if the AL gets a little interleague edge, then if you take the whole window as representing an even balance, this year the leagues are uneven. This year, I don’t know how you could demonstrate that the AL isn’t the better of the leagues.

Some points of possible interest: this year, the average AL team had an opening-day payroll a little under $2 million higher than the average NL team. Last year, the average NL team was higher by a bit more than $2 million. But in truth, this doesn’t mean anything if you don’t take service time into account.

And then, pulling from Man Games Lost, this year the average NL team has lost 776 games to injury. The average AL team has lost 676, exactly 100 fewer. But right now we don’t have a good measure of how important those missing games have been. It’s a partial explanation for the discrepancy in success. I’m skeptical it’s a big one.

Cherry-picking, five teams in the National League stand out, in a good way. I’m referring to the Cardinals, Dodgers, Mets, Cubs, and Pirates. Those teams have won 53% of their interleague contests, which is good. But then, they’ve won 60% of their intraleague contests, which is much better. So they’ve run into some obstacles. As expected, the AL has beaten up on the NL’s dregs. This year’s dregs are really dreg-y. Should be better next year, but, I don’t really know.

In closing, if you want a neat little way to think about this, we can make use of the Log5 equation. Let’s take just this year’s AL interleague winning percentage. If you think that reflects real ability, then the AL would be a “true talent” .525 league, and the NL would be .475. So the average interleague game would be like an 85-win team playing a 77-win team. Let’s now say, instead, you believe more in the Pythagorean record. Then it’s more like an 87-win team playing a 75-win team. The difference between the leagues has been big. It’s existed for a while, now, but this year it’s grown. I don’t know if it’ll stay like that, or if it’ll go back down. I don’t know when the NL will appear superior. I’m sure it’ll happen. It’s just not happening at the moment.