Mains: How many runs win a game?

From SABR member Rob Mains at Baseball Prospectus on January 11, 2018:

One of the key sabermetric principles is that 10 runs roughly equals one win. Former BP editor-in-chief Ben Lindbergh wrote this in his 2013 Grantland article about the pitch framing wizardry of Jose Molina:

… Molina has saved his teams 111 runs—or, using the standard 10-runs-to-a-win conversion, about 11 wins—because of his framing from 2008 to 2013.

Ten runs to a win may be standard, but it sure isn’t intuitive. You need 10 runs to win a game? Teams scored 10 or more runs in a game only 422 times last year. That’s fewer than nine percent of all games. And they won 405 of those games, for a .960 winning percentage. Why do you need 10 runs? Why not seven? Teams that scored seven runs won 83 percent of the time. Or six? Those teams won 72 percent of their games. Or five: 62 percent. Four’s the dividing line; teams that scored four runs in 2017 lost more than half of their games. But why 10? That’s twice five, and teams scoring five won nearly two-thirds of the time.

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Originally published: January 11, 2018. Last Updated: January 11, 2018.