The Mariners lost two of three to the Dodgers over the weekend. It wouldn’t be fair to say the series was an accurate representation of the Mariners’ season, but it works as a convenient caricature. On Friday, the Mariners lost to the Dodgers by ten. On Sunday, the Mariners lost to the Dodgers by eleven. On Saturday, the Mariners beat the Dodgers, by one, in the tenth inning, on a walk-off balk. The Mariners avoided a sweep, and, indeed, the Mariners actually still have a better record than the Dodgers do. Over the three games, though, the Mariners were outscored by a margin of 27-7. Sunday was the Mariners’ worst loss of the year.

It’s hardly new information that the Mariners’ winning percentage and their run differential don’t exactly match up. This has been true for a matter of months, and it partly helps to explain why the AL West is as close as it is. But before we all just collectively get used to something, we should take a step back so we can reexamine precisely what’s been going on. Although the Mariners have slipped out of playoff position, they’re still within striking distance of both the A’s and the Astros. The Mariners are 3.5 back in the wild-card hunt, despite a run differential of -42. The Rays are 7.5 back of the Mariners, with a run differential of +10. The Angels are 8.5 back of the Mariners, with a run differential of +39. The Twins are 11 back of the Mariners, with a run differential of -22. Every year, there are run differential overperformers and underperformers. Yet this is far more extreme than is typical.

The last time I took a look at the Mariners was July 3. Through play on July 3, the Mariners had baseball’s fourth-best record. However, they had baseball’s 11th-best run differential. It was easy, at that point, to say the Mariners were due for a bit of regression. In a sense, they have regressed. And yet the numbers still look bizarre. Since play on July 4, the Mariners have baseball’s seventh-worst record. They also have baseball’s very worst run differential, worse even than the terrible Marlins (and, by definition, everyone else). A team’s Pythagorean winning percentage is simply its winning-percentage estimate based on runs scored and runs allowed. Through July 3, the Mariners were beating their Pythagorean estimate by 109 points. Since July 4, as the Mariners have slumped, they’ve still beat their Pythagorean estimate by 83 points. You could say even the bad Mariners have overachieved.

I live to put baseball data in context, so I’m going to return to an image I embedded in that linked post above. This is updated through the present day. In this plot, you’re going to see every team-season since 1900, expressed in terms of overall winning percentage, and run differential per game. The 2018 Mariners are the dot in yellow. The data sample numbers 2,520 team-seasons.

This plot illustrates a fundamentally obvious baseball principle: Good teams tend to outscore their opponents. Even though it’s easy to understand how, in theory, a team’s winning percentage and run differential might diverge, in truth the former has an established tendency to follow the latter. I don’t think I need to cover that ground. You already get it! The linear relationship in that image is apparent. The Mariners stick out. They stick out in part because I put them in yellow, sure, but the 2018 Mariners have been legitimately weird. How weird? Here’s a table of the top ten Pythagorean overachievers since the turn of the previous century:

All-Time Anomalies (1900 – 2018) Team Year Win% Pythag% Difference Mariners 2018 0.568 0.466 0.102 Athletics 1955 0.409 0.319 0.090 Reds 1981 0.611 0.523 0.088 Cubs 1907 0.709 0.623 0.086 Rangers 2016 0.586 0.505 0.081 Tigers 1905 0.516 0.435 0.081 Diamondbacks 2005 0.475 0.399 0.076 Angels 2008 0.617 0.543 0.074 Dodgers 1954 0.597 0.525 0.072 Padres 2017 0.438 0.366 0.072

The Mariners are still holding on to that first-place ranking. For something similar, here’s another top-ten table. For this one, I’ve taken the absolute values of the differences between winning percentage and Pythagorean estimated winning percentage. This way, underachievers and overachievers are grouped together.

All-Time Anomalies (1900 – 2018) Team Year Win% Pythag% |Difference| Mariners 2018 0.568 0.466 0.102 Yankees 1931 0.614 0.705 0.091 Mets 1993 0.364 0.455 0.090 Athletics 1955 0.409 0.319 0.090 Reds 1981 0.611 0.523 0.088 Cubs 1907 0.709 0.623 0.086 Browns 1905 0.353 0.435 0.082 Pirates 1917 0.331 0.413 0.082 Athletics 1946 0.318 0.400 0.082 Pirates 1986 0.395 0.477 0.082

Since 1900, the biggest difference between a team’s winning percentage and its Pythagorean winning percentage has been 91 points. The 2018 Mariners are hanging around at 102 points, more than three-quarters of the way through the year. Based on our current projections, the Mariners are going to finish with a final difference of 78 points — still historically significant, if no longer the most extreme anomaly. But our projections don’t really attempt to figure out run-differential overachievers and underachievers. The Mariners don’t have to be *that* weird the rest of the way to look like one of the strangest teams that anyone’s ever seen.

In the first table, you might’ve spotted some teams from recent seasons. The 2017 Padres were a big Pythagorean overachiever, and so were the 2016 Rangers. As such, you might wonder if we’re seeing more divergence of late. The long and short of it: no. There’s no evidence to suggest that teams have now figured out ways to beat their run differentials. For every individual team-season, I found the absolute value of the difference between its winning percentage and its estimated winning percentage. Here are the average and median differences, broken down by decade:

Nothing there to be seen, I don’t think. It’s all held pretty steady. Sure, teams now operate in ways different from how they did before, but the goal has always been to get good, and getting good involves outscoring the other team more often. I don’t think anyone has unlocked the key to being an overachiever. I mean, yeah, the key is being better in the clutch, but that’s never been proven to be a sustainable skill. Perceived advantages can disappear in the blink of an eye.

We’re getting away from the Mariners, now, so let’s bring it back. Here’s what their season looks like, in terms of rolling winning percentage and rolling Pythagorean winning percentage:

After the second game of the season, the Mariners had a winning percentage of .500, and a Pythagorean winning percentage of .500. Since then, they’ve been an overachiever every single day, with little in the way of evident regression. In this last plot, I’m just going to show you the rolling difference between those two lines. I’ve also included a flat line at .091 — remember that the 1931 Yankees finished with a winning percentage that was 91 points removed from their Pythagorean winning percentage. That’s the present record for the biggest all-time gap.

Those are the Mariners. Their winning percentage has never once dropped below their Pythagorean winning percentage. The gap has been enormous since the third game of the year. The Mariners might not finish with the biggest gap of all time, and, in fact, they probably won’t finish with the biggest gap of all time, based on the projections, but they’re going to be close. Just a couple weeks ago, the Mariners had a gap of 88 points. It’s now up to that previously-noted 102, thanks in part to what happened against the Dodgers. Another series or two like that and the Mariners will be on a collision course for history.

We can already say that, historically, the 2018 Mariners appear unusual. The only thing we don’t really know is whether they’ll come out as the most unusual. It’s another thing to monitor over the season’s final several weeks. Because of how well the Mariners have hit in the clutch, and because of how good Edwin Diaz has been at closing games, the Mariners remain alive in the playoff hunt. Catching up to the next-best team is, of course, the highest priority. But even if the Mariners do wind up on the outside looking in, they could also end up as the most anomalous team in modern baseball history. Depending on how you look at it, that could be either a good thing or a bad thing. There’s no debate that it would be an interesting thing.