Is quality start really a quality stat?

A starting pitcher is credited with a quality start when he pitches at least six innings and allows three or fewer earned runs. Some opponents of the stat argue that pitching six innings and allowing three runs produces a 4.50 ERA, hardly quality. However, an ERA of 4.50 comes in below the overall American League ERA in 2003 (4.52) and it’s rare that a pitcher pitches exactly six innings and allows exactly three earned runs. The game ERA drops below 4.00 as soon as the pitcher reaches seven innings in a quality start.

Quality starts occur in less than half of the games started by pitchers (47% through 9/26). The key quality feature of the quality start is that a team that has a pitcher throwing a quality start can expect to win about two-thirds of their games. That’s an excellent .667 winning percentage. And when you consider that two opposing pitchers can earn quality starts in the same game while only one can earn the victory, it makes the .667 winning percentage all the more impressive.