A quality start refers to when a starting pitcher goes at least six innings while giving up three earned runs or less. Sportswriter John Lowe of the Philadelphia Inquirer coined the term in 1985. While a quality start does not guarantee that a pitcher will walk away with a winning decision for the game, it implies that he has put his team in a position to win the game. Critics of the statistic argue that 3 earned runs in six innings translates into a 4.50 ERA. In spring 1992, however, David W. Smith published an article pointing out that from 1984 to 1991, the average ERA in a quality start was 1.91, indicating that 3 earned runs in six innings was at the extreme end of the spectrum, rather than the norm.
In 1995, Greg Maddux recorded 24 quality starts out of 25 games pitched, giving him the highest single-season quality start percentage (96%). Thus far in the 2014 season, Dodgers pitcher Clayton Kershaw leads the league with 19 quality starts in 21 games (90%).
Clayton Kershaw (LA Times)