One of the things Bill James popularized years ago was the idea that a team's run differential could be a great predictor of a team's record. By looking at the number of runs scored and runs allowed, plugged into the Pythagorean Theorem, you can come up with an approximate number of wins a team should have.
He called this new record third-order wins, but it's been simplified to Pythagorean Record by sites like Baseball Reference. BBRef even has a handy section on its standings page, tracking runs scored, runs allowed, pythag record and the difference between it and the team's real record.
Why is that important? If we look at a team's pythag record as its expected record, we can easily tell how lucky or unlucky a team has been. Some teams can consistently outperform their pythag record. The Angels, for instance, were semi-famous for doing just that for three or four seasons. Houston did the same thing last season, which is pretty sad considering how bad the Astros record was.
Let's look at the National League right now to see which teams are outperforming their pythag records and who is struggling there. Here's a link to the standings page at BBRef.
The luckiest teams right now are all outperforming their expected records by a game. Colorado, Philadelphia, Florida, Chicago, Pittsburgh and the Dodgers are all one game better than they would be expected. That's a pretty small number compared to how many teams are underperforming.
The team with the worst luck so far is St. Louis, the current NL Central leaders. The Cardinals are three games below their expected record. They're also the only division leader in the National League to have a negative differential there.
Atlanta, New York, Cincinnati and San Diego are all two games worse than expected. The Padres and Mets sit at the bottom of their divisions while Atlanta is next-to-last in the NL East. Cincinnati is only a game back of St. Louis in the Central, but with the Cards expected record, it's going to be hard for Cincy to catch them any time soon.
The only team who's performing as expected to this point is Washington, who is 10-10 and sits in third place in the East. Washington hasn't had a .500 record since 2005, the first year in Washington after the franchise moved from Montreal.
It's still very early to put much stock in these expected records, but we can definitely get a sense of which teams are for real and which are not. It appears that St. Louis falls into the former category, which doesn't bode well for Houston's upcoming series against the Red Birds.