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MLB's next big thing: Run differential might be losing ground

Based on run differential, the Mariners should be a sub-.500 team. Instead they're on the fringe of playoff contention. Kevin Jairaj/USA TODAY Sports

Something is afoot with run differential. That's the answer, so let's jump back to the question.

Do you ever get an email (or text or telegram or any other form of communication) to which your knee-jerk response is an audible "Excuse me?"? I got one of those the other day. The message posed this question, which I am paraphrasing: How much have all the blowouts this season contributed to the declining impact of run differential?

Excuse me?

Run differential is everywhere in baseball these days, its influence on our perception of the game growing gradually ever since the 1980s, when Bill James pointed out the strong correlation between how many runs a team scores and allows, and its winning percentage. There's a lot behind the theory, and if by chance you're not up on it, here's a primer.

For me, the most important thing to bear in mind is that a team's run profile is a better indicator of its future fortunes than its won-lost record. That has the double consequence of also being a better indicator of underlying talent. It's an important lesson to take to heart -- unless the lesson is no longer true.

Typically, by the time we get through a full season, and random variables have started to even out, the final standings tend to dovetail a great deal with team-by-team run differentials. But there are always differences, some small, some historically large. Run differential is not an absolute predictor, and one of its great functions is to lead us into investigations of why a team's profile might not be accurately reflected in the standings.

Getting back to that emailed question, is run differential really declining in impact? What would even spur such a question? Before I could even ponder the former, I had to wrap my arms around the latter. Why would this person even suggest such a thing?