In baseball, a quality start (QS) is a statistic for a starting pitcher defined as a game in which the pitcher completes at least six innings and permits no more than three earned runs. The term was coined by John Lowe, a sportswriter for the Philadelphia Inquirer, in 1985 as a means to gauge whether a pitcher did his job. The quality start statistic helps to quantify which pitchers did a "quality" job in preventing runs and getting outs. A starting pitcher records a quality start when he pitches at least six innings and allows three earned runs or fewer. The advantage of this statistic is that it does not punish a pitcher who suffers from a low run support the way a win-loss record does. If a pitcher allows one run but his team is shutout, his quality start percentage will increase, but his win percentage would decrease with the loss. However, this statistic is also unfavorable to pitchers who pitch deep into the ball game. If a pitcher pitches six innings and gives up three runs, they get a quality start with an ERA of 4.50. However, if they pitch a full nine innings and give up four runs, they would have an ERA of 4.00, but not get the quality start.

In summary, a quality start is a statistic in baseball that measures the performance of a starting pitcher. It is achieved when a pitcher completes at least six innings and allows no more than three earned runs. The statistic helps to quantify which pitchers did a "quality" job in preventing runs and getting outs.