(Photo by Jonathan Newton / The Washington Post)

The Washington Nationals clinched their second National League East title in three seasons last night. The Baltimore Orioles also clinched, the first time they did so at home since 1979. That means we have the chance at seeing a Parkway Beltway World Series.

According to Fangraphs, the Nats have a 35.1 percent chance at making the World Series, while the Orioles sport a 18.8 percent chance. That means there is a 6.6 percent chance at these two meeting for all the marbles, or 14-to-1 odds.

But what’s the easiest path for them to get there?

Using a Bill James method known as log5, we can find an expectation for one team’s performance against another. Log5 predicts Team A’s win percentage against Team B with the following formula:

p(Team A Win) = Team A_win% *(1 – Team B_win%)/(Team A_win% * (1 – Team B_win%) + (1 – Team A_win%) * Team B_win%)

We could refine the above formula more by including home-field advantage, but for the purposes of this post we can keep it simple. Also, instead of using straight winning percentage in the calculations, it is better to use a win percentage derived by BaseRuns, which gives a clearer picture of the true talent a team has.

Base Runs is a team context formula, like Runs Created. It tries to measure the interactivity between offensive events, not just the simple linear values. The basis for BsR is that runs scored equals home runs plus the number of baserunners times the percentage of baserunners who score.

For example, if the season ended today, the San Francisco Giants (0.537 BaseRuns win percentage) would face off against the Pittsburgh Pirates (0.551 BaseRuns win percentage) in the NL wild-card game. Using log5, we would estimate that the Pirates would win 51.4 percent of the time.

But after the wild-card game, a team needs to win three of five to advance and then five of seven. To figure out those probabilities the math gets slightly more complicated, since we have to factor in all possible winning scenarios. For instance, a five-game series could have one of the following scenarios:

  • Team wins series 3-0 in three games
  • Team wins series 3-1 in four games
  • Team wins series 3-2 in five games

We can calculate the probability of all these outcomes using the following formula: PA  =  p3(1 + 3q + 6q2)

For a seven game series, the formula becomes PA  =  p4(1 + 4q + 10q2 + 20q3).

Here are the probabilities the Nationals win a five and seven game series against their most likely playoff opponents.

Here is the same for the Orioles.

So for the Nats, the easiest path to the World Series is to face the Giants, then Cardinals. Baltimore fans want to root for the Royals and Tigers.

Now all that is left is settling on what to call this thing.