The Nationals head to Fenway Park for a weekend series with the Red Sox. The teams traded roles, as Washington is the first place team and Boston sits in last:

This weekend should indeed be fun. Stephen Strasburg could throw 100 miles per hour in a park that’s 100 years old. Bryce Harper will try to put his dent in the Monster. Michael Morse will take aim at Landsdowne Street. And the Nationals will try to hold off the Red Sox. They’re in last place, but they’re a game over .500 at 29-28 — and their plus-26 run differential is only one run worse than Washington’s.

I’ll be going to Sunday’s game pitting Jordan Zimmermann against Jon Lester. Needless to say, Boston spectators are extremely excited about Bryce Harper coming to town:

By the way, that’s Rebecca Tilney, a classmate from college, in the role of the mom.

I think the run differential stat is an interesting one. Boston score 297 runs and allowed 271. The Nationals scored 209 runs and allowed 182. Not all run differentials are the same. In lower run environments, the same difference will produce a higher expected winning percentage. Boston’s expected won-lost record is 31-26, two games better than their actual record. The Nationals should be 31-24, one game worse. So with nearly the same difference in runs scored and allowed, the Nationals are a slightly better team. Note two, the Nationals are 12-9 in one-run games, the Red Sox 5-7. With great pitching and low scoring, the Nats play a lot of close games, and so far those have worked to their advantage.