Posted by Andy on August 30, 2011
A Quality Start is an official stat assigned to a starting pitcher who goes at least 6 innings while giving up no more than 3 earned runs. Let's take a look at this stat in a bit more detail to see if it's all that useful.
Here is the fraction of all starts going back to 1919 that were Quality Starts, using the definition as stated above:
Like a lot of pitching stats, this one peaked in the 1960s and 1970s when scoring was quite low. It dropped dramatically in 1987 when home runs were hit at a record pace. In 1993, there was a sudden drop from 53.6% to 50.4%, and the rate continued to fall each of the next 3 years. Over the course of the steroid era, the QS% bounced between 46% and 51%. Then, in 2010 and 2011, as run scoring has dropped again, QS% has increased dramatically to pre-steroid era levels. This year's rate of 54.2% is the highest since 1988's 56.4%.
But are quality starts helping teams win? Here's the percentage of team victories when their starter throws a quality start:
The win percentage was around 70% for the first half of the 20th century. It started to drop in the 1960s as more and more quality starts were being thrown (see the first graph). Then in the steroids era, the win % started to climb again. That makes sense--when run scoring was up, if your pitcher was good enough to give up no more than 3 runs over 6 innings, you had a pretty decent shot at winning. The win rate peaked in 1996, reaching nearly 70% for just the second time since 1958 (with the other being the HR-aberrant 1987). But as scoring has fallen off in recent years, the team win % in quality starts has fallen off too. This year's rate of 66.0% very slightly lower than 1981 and 1976's rates, and the last year lower than 2011 was way back in 1972.
If we look at 2011 teams with the most pitchers throwing at least 10 quality starts
, it shows that the stat is a bit flawed. Among the leading teams (with 5 such pitchers) are the Reds, Twins, and Pirates, all teams that are near or below .500, with the Twins in particular having a surprisingly poor record despite all the quality starts. Meanwhile the Red Sox have just two pitchers with 10 quality starts and yet are one of the best teams in baseball. Another near-playoff team, the Angels, have just 3 pitchers with 10 quality starts.
The quality start stat is interesting, but only at a surface sort of level.