Quality Start

The Quality Start is a relatively new statistic devised by sportswriter John Lowe in an attempt to evaluate the performance of starting pitchers in terms other than the traditional values of ERA and wins and losses.

A starting pitcher is credited with a Quality Start if he pitches at least six innings and allows three or fewer earned runs. The original motivation for the present study was to pursue a statement written by Bill James in the 1987 Baseball Abstract.

While discussing some of the pros and cons of Quality Start as a statistic, he noted that there had been criticism (by Moss Klein, writing in The Sporting News) of the Quality Start in that it would be possible in principle for a pitcher to go exactly six innings in every start and allow exactly three earned runs each time, compiling an ERA of 4.50, although each start would be categorized as a Quality Start.

Moss that this possibility invalidated the entire concept. Bill thought Klein's criticism was an unreasonable extreme example and he ventured that "...I doubt that any pitcher had an ERA higher than 3.20 in his Quality Start." My intuition on this point agreed with James', so I decided to pursue the question by using the Project Scoresheet data base, which covers all Major League games played from 1984 through 1991. Bill was right about the ERA of pitchers in Quality Start, but there are in fact other interesting conclusions as well”.

The conclusion seems clear that Quality Start, taken in the aggregate, reflect much better than average performances and that, in the aggregate, Quality Start correlate with team winning percentage. Furthermore, these good performances are also of longer duration, meaning that the bullpen is given some rest when a Quality Start is taking place. What about Moss Klein's concern about the "minimum" Quality Start, with its ERA of 4.50?

Over the last eight seasons, there have been 17457 Quality Start, and 989 of them have been exactly six innings with three earned runs. On a percentage basis, which is called the "Klein percentage", this is a value of 5.7%. Moreover, there are five categories of Quality Start which occurred more often, all with substantially better ERA. It's pretty clear that Moss has missed the significance of Quality Start by his concentration on the extreme case.