Why do some relief pitchers seem to produce ERAs that are a long way off their real ERA?
We’ve found that it takes 10 or more full seasons for the luck to be squeezed out for everyday players and starting pitchers. In other words, if you run ten season replays and average the results, the Diamond Mind stats are an almost exact match for the real-life stats, even though some of the individual seasons are a little high or a little low. But 10 full seasons for a relief pitcher involves only 2-3 seasons worth of innings for a starter. That means relief pitching stats are going to be a lot more volatile just because of limited playing time. An extra pair of three-run homers over the course of a season will add almost a full run to the ERA of a reliever who pitches only 60 innings per year.
