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The NL Is Finally Winning Interleague Play — For Now

I don’t want to say it’s been a while since the National League broke even in interleague play, but here are some things that were true the last time it happened:

  • George W. Bush was still in his first term as president.
  • Barry Bonds was the best player in baseball.
  • We were all excited about the idea of a sequel to “The Matrix.”
  • Beyonce was just trying out the whole solo thing.
  • Battle lines were drawn between Ruben Studdard and Clay Aiken supporters.

You get the idea. Between 2003 and this season, AL teams compiled a 1,765-1,465 record1 against their NL counterparts — good for a .546 winning percentage, or roughly 89 wins per 162 games — and won interleague play by a grand total of 1,688 runs. It’s a run of complete dominance that has covered more than half the history of regular-season interleague play (which began in 1997).

At a team-by-team level, the difference between leagues has been downright comical at times. In 2009, at the peak of the AL-NL disparity, the AL’s 75-win Toronto Blue Jays had a better schedule-adjusted run differential2 than the NL’s 93-win Philadelphia Phillies. Last season, the 98-win Pittsburgh Pirates were dead-even with the 78-win Boston Red Sox. Talent being equal, being in the NL over the past decade-plus has consistently been worth a number of extra wins each season.

But so far this year, the NL has done uncharacteristically well against the Junior Circuit, posting a 25-18 record in interleague play as of Monday night’s games. If it holds up, that .581 winning percentage would represent the NL’s best-ever performance against the AL, shattering the old mark of .548 set in interleague’s debut season.

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However, we’ve seen this kind of fast start from the NL before. In 2014, NL teams won 26 of the first 43 interleague matchups, a game better than even this season’s fast start, only to go 115-149 over the rest of the season and finish the year with a lousy .459 winning percentage. That was one of four instances during the NL’s 12-year run of futility that the Senior Circuit was above .500 through 43 interleague games; it finished those seasons with an average winning percentage of .453.

And there are signs that this season could be destined for more of the same. Although the NL is home to a handful of the best teams in MLB — the mighty Cubs, plus the Mets, Nationals, Dodgers, Cardinals, Pirates and Giants, all of whom rank among FanGraphs’ top 11 teams by projected wins above replacement going forward — it also houses each of the seven worst teams in baseball by projected WAR.3 So despite the NL’s top-heaviness, our team Elo ratings (which estimate a team’s strength at any given moment) consider the gap between the average AL and NL teams to be bigger now than it usually is after 43 interleague games.4

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That’s why Elo’s predictions say the AL should actually be ahead on wins, 22-21, against the NL right now. And since ‘97, that Elo-generated expectation has been a better predictor of interleague play over the rest of the season than each league’s actual record through 43 games.

In other words, the NL shouldn’t start celebrating quite yet. Even though it’s off to a strong start against its cross-league rival, there’s still plenty of time left for the AL to mash it into paste, as usual.

Footnotes

  1. Including the World Series.

  2. As measured by Baseball-Reference’s Simple Rating System, or SRS.

  3. For those curious, that’s the Diamondbacks, Rockies, Padres, Brewers, Reds, Phillies and Braves.

  4. Granted, MLB used to start the interleague schedule later in the season; before 2013, it would be mid-June before 43 games were played. But since Elo ratings are theoretically time-independent (hence the “strength at any given moment” part above), that difference shouldn’t be affecting the results.

Neil Paine is a senior sportswriter for FiveThirtyEight.

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