}}}In baseball statistics, earned run average (ERA) is the mean of earned runs given up by a pitcher per nine innings pitched. The ERA tells the average number of runs a pitcher would inadvertently surrender over the course of a full game had he been kept in. It bears similar meaning to a hitter's batting average. It is determined by dividing the number of earned runs allowed by the number of innings pitched and multiplying by nine. Runners reaching base on errors (even errors by pitchers) do no