Mains: The state of the quality start

From SABR member Rob Mains at Baseball Prospectus on November 20, 2018:

As I discussed last week, one of the seven things you (probably) didn’t know about the 2018 season is that quality starts—defined as a start lasting six or more innings with three or fewer earned runs allowed—as a percentage of total starts cratered to an all-time low of 41 percent. I want to look a little more deeply into this, since it’s been a while (May of 2016, to be exact) since I’ve examined quality starts.

The term quality start is credited to Philadelphia Inquirer sportswriter John Lowe. It’s been derided every since he coined it in December of 1985. Three runs in six innings? That’s a 4.50 ERA! In what world is that a measure of quality?

Let’s start with that criticism. It’s true that 3 x 9 / 6 = 4.5. (You came here for this sort of high-level math, right?) But it’s also true that type of start, meeting the bare minimum for earning a quality start, is unusual. Here’s the proportion of quality starts in which the pitcher lasted exactly six innings and yielded exactly three earned runs. (I’m going to confine this analysis to the 30-team era, 1998-present. Almost all data retrieved in this article is via the Baseball-Reference Play Index.)

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Originally published: November 20, 2018. Last Updated: November 20, 2018.