The 2018 Red Sox in Historical Context

As soon as any World Series is over, it’s fair to wonder how the most recent champion stacks up when compared to the history. And while sometimes the numbers are downright laughable, the 2018 Red Sox have been pretty extreme. In the regular season, they won five more games than anyone else. In the playoffs, they lost just once per series while eliminating the three other best teams in the game. Sometimes, you think about the history because you think you’re obligated. In this case, we look to the history because it seems like the Red Sox might’ve done something historic. It feels like this might’ve been one of the all-time greats.

I’ve run some numbers in order to see what we’ve got. I should acknowledge right here there’s no perfect, agreed-upon way to do this. There’s no ideal measure of a team overall. Does it matter how good a team is for seven months, or is it only the playoffs that matter, provided you do just enough to make it in in the first place? There are arguments to go in either direction, but for my purposes here, I’ve simply combined regular-season numbers with postseason numbers. The postseason sample, of course, is dwarfed by the regular-season sample, but that’s how I feel like it should be. You might have another opinion, and so you might trust your own analysis. Below, I’ll quickly present my own.

Just about all the information here comes from Baseball Reference, and I’ve pulled data going back to 1903. I’ve decided to focus on four team statistics. They are:

1. overall winning percentage
2. overall run differential per game
3. overall winning percentage, z-score
4. overall run differential per game, z-score

The first two, I think, are pretty obvious. Of course I should be looking at winning percentage, and then run differential is another marker of dominance. The latter two are less obvious, but by looking at z-scores — the number of standard deviations from the league mean — we’re able to get an idea of exceptionality, if you will. It’s more notable if a team stands out from a league otherwise characterized by parity. Here’s how the league winning-percentage standard deviations have moved since around the turn of the last millennium:

The league is less spread out than it used to be, but we also just saw the largest spread since 2002. Baseball in 2018 had very clear tiers. Here’s how the league run-differential standard deviations have moved since around the turn of the last millennium:

Same pattern, naturally. Used to be, ages ago, the difference between good teams and bad teams was more stark. We’ve seen a general trend toward parity, but, again, in 2018, the spread here was the biggest it’s been since 1956. In this most recent season, there were haves, and there were have-nots. The Red Sox were one of the haves. It’s fair to say the middle class was under-populated.

Anyway, that’s all the background. Now here is how the 2018 Red Sox measure up. I’m showing this in terms of percentile rankings out of all team-seasons. There are nearly 2,500 team-seasons in the sample. Spoiler: The Red Sox were very good.

We can go in order. Looking over almost 120 years of baseball, this year’s Red Sox ranked in the 99th percentile in winning percentage. They ranked in the 98th percentile in run differential per game. Looking at the same, except expressed in z-scores, the Red Sox ranked in the 99th and 97th percentiles, respectively. Tremendous season. One of the better seasons. The numbers here are in agreement.

But now let’s take a possibly controversial stance. What if we compare the Red Sox only to other champions? There have been 114 champions. What if we take the stance that, in order for a team to be truly historic, one of the all-time greats, it has to win it all? Here is the same plot, only this time, we’re comparing the 2018 Red Sox only to their title-winning predecessors.

The bars get lower, of course, because we’ve eliminated all the bad baseball teams. Still, among all previous World Series champions, the Red Sox look good across the board. Their percentiles are 86th, 80th, 86th, and 75th, respectively. There’s not quite enough to say the Red Sox are clearly one of the very best champions in history, but they’re in the best, say, 15 – 25%. Which is pretty damn terrific, when the peer group is all winning teams. There’s no shame in being far superior to the average champ. Especially in this modern era of super-teams.

The following table is split in two halves, even if it’s not very obvious. On the left, the 25 highest winning percentages of all time. On the right, the 25 highest winning-percentage z-scores of all time. In each case, the Red Sox are highlighted in yellow.

On the left, in terms of raw winning, the Red Sox haven’t been surpassed by many champs in what we can consider the more modern era. On the right, more recent teams are better represented, as the leagues have become more even. There are reasons one might prefer either measure. The one on the left is elegant in its relative simplicity.

To whatever extent the Red Sox haven’t often been regarded as one of the best teams ever, during and after the season, it’s probably because of the stratification of the leagues. There were a number of very good teams, in part because there were a number of very bad teams, and among those very good teams, the Red Sox weren’t extraordinary. They got somewhat lost in the crowd, as some attention would’ve gone to the Yankees, and the Astros, and so on and so forth. Still, the Red Sox were legitimately terrific, and obviously, they strengthened their case all the more by breezing through difficult competition in October. The 2018 Red Sox were great. They wound up very deserving champions. They’re not the best champion ever, and they might not be all that close to being the best champion ever, but even as champions go, few teams have been so good for so long. You couldn’t really ask for a more impressive seven months.