Why the Red Sox won't win the World Series

(Greg M. Cooper/USA TODAY Sports)

No, it’s not because of their bullpen. Without going into a lot of deep analysis, simply put it’s because there are 10 teams in the playoffs. The Red Sox may have the best one, and may have the best probability of winning it all, but it’s still far from a sure thing, or even a likely thing. 

Read on….

The Atlanta Braves made the playoffs 14 seasons in a row from 1991 to 2005, but only won the World Series one time and were considered a disappointment because of it.  With eight teams making the playoffs, on average, a team will win once every eight times it gets in there (slightly more if they’re better than the average playoff team, slightly less if they’re worse). Fans and baseball analysts usually grossly overstate this “slightness”.  More on that in a minute. Anyways, the Braves would have been expected to win 1.75 times out of those 14. If they had won twice they would have actually exceeded the expected.

But, if they were always the best team in the league surely they should have won more often, you may think. But not necessarily. As I alluded to above, most people overestimate the advantage a better team has over an inferior one. Sure, the better team is more likely to win, but the advantage is typically small. It’s rare in a playoff series to have a team be expected to win with more than a 60% probability.


As I have explained before, the probability that one team beats another in a single game can be approximated by adding 50% to the difference in their winning percentages. e.g, a .500 team is going to beat a .400 team 60% of the time, and lose to a .600 team 60% of the time. (Note: this obviously ignores home field advantage, pitching matchup, injuries, and so on. It’s a model meant to be useful at a macro level).  Playoff teams typically have very similar win-loss records. Sure, a 102 win team sounds much better than an 88 win team, but in terms of winning percentage, it’s like a 10-6 football team playing a 9-7 team. The 9-7 team might not be favored, but it wouldn’t be a shock if they won.

Let’s use some actual numbers with this year’s Red Sox: The hardest path to duck boats would involve beating the 100 win Yankees, 103 win Astros, and 97 win Brewers in the LDS, LCS, and World Series. The probability of beating the Yankees in a given game is about 55%. Extrapolating some math for a best 3 out of 5 shows that Boston will win 3 before New York does about 59% of the time. The numbers for Houston are 53 and 56%, and Milwaukee is 57 and 65%.  Therefore the probability of winning all these series is 59% x 56% x 65% = 22%. Even though we would be favored to win each individual series, there is less than 1 in 4 chance that we’d actually win all of them.
Luckily, we won’t necessarily have the toughest road ahead of us. Maybe Oakland will beat New York, or Cleveland will upset Houston.  And the Rockies end up winning the NL pennant. In that scenario, we would win all three series 29% of the time. Huh! A seemingly much easier route doesn’t make that much of a difference.

When you take into account for the probabilities of our potential opponents, and work out the math, the Red Sox have a 26% chance of winning it all. See full results for each team below

{By the way - copy of this fillable spreadsheet where you can play around and see how the probabilities change depending on how many wins your team or their opponents have is available for the asking}

Now, these are higher odds that any other team, and if I was forced to bet my life savings on one team, the Red Sox would be it. But there’s still an almost 3/4 chance that they won’t win it all. So, if there is a November parade which does not include duck boats, don’t be too disappointed.