What is a real "quality start?"
MLB defines a quality start as:
A starting pitcher records a quality start when he pitches at least six innings and allows three earned runs or fewer. A starting pitcher has two jobs: to prevent runs and get outs. The quality start statistic helps to quantify which pitchers did a "quality" job in those two departments.
This definition of a "quality" yields an absurd result: a pitcher who allows three earned runs over six innings would have an ERA of 4.50 -- not good -- and yet he still receives a quality start.
Bill James addressed this in his 1987 Baseball Abstract, saying the hypothetical example (a pitcher going exactly 6 innings and allowing exactly 3 runs) was extremely rare among starts recorded as quality starts, and that he doubted any pitchers had an ERA over 3.20 in their quality starts. This was later confirmed through computer analysis of all quality starts recorded from 1984 to 1991, which found that the average ERA in quality starts during that time period was 1.91.
Former pitcher Carl Erskine said "in my day, a quality start was a complete game ... you gave everybody a day's rest." This view was also echoed by Fergie Jenkins who often said that it was his job every time he took the job was to have a complete game win. If he was going against an opponent like Bob Gibson, he knew that he could only give up one or two runs tops in order to win the game.
Growing up, it was the consensus gold standard for a pitcher to have an ERA under 3.00.
To get to that level, a pitcher would have to have these types of starts in order to get the win:
5 IP 1 ER = 1.80 ERA
6 IP 2 ER = 3.00 ERA
9 IP 3 ER = 3.00 ERA
2.57 ERA for 7 IP with 2 ER, but 3.86 ERA with 3 ER.
2.25 ERA for 8 IP with 2 ER, but 3.36 ERA with 3 ER.
Therefore, a quality start should be a scaled event for starting pitchers at points of 1, 2 and 3 earned runs allowed to get under 3.00 ERA.
The oddity in this analysis plays into the rise in the bullpen managed game. A starter with 1 ER in 5 IP can be pulled for a shut down bullpen of under 2.00 ERA to get under a 3.00 ERA for the entire game. Stat men claim that starter's batting average against climbs dramatically when facing a hitter the third time in a game. Managers are not only managing the pitch count but also the number of times through the batting order.
Conclusion: a quality start should be any start that yields a 3.00 ERA or under.