Earned run average is a useful statistic, but it can't be trusted in small samples. It has little predictive ability over short spans of time, given the number of things that can influence it: defense, park effects, batting average on balls in play or just plain dumb luck. When enough innings are looked at together, ERA has its merits, but with less available data a run estimator -- such as SIERA -- is the better bet for year-to-year predictions. SIERA is a metric created by Baseball Prospectus that generates a pitcher's ERA while bypassing the events that could fall under the defense or luck subheadings, such as batting average on balls in play.
That means SIERA is useful for seeing which players over or underperformed in terms of their ERA. Using this tool, we can predict some likely 2011 sleepers and some pitchers who will miss the good old days when extra luck and quality defenses saved them inning after inning. Each player is listed with his 2010 stats. If a player's SIERA is much higher than his ERA, he is a bounce-back candidate and vice versa.
Beckett signed a lucrative long-term extension with Boston at the start of the 2010 season and subsequently pitched like a guy looking to get released. His 5.78 ERA was a career worst, and he posted his lowest strikeout to walk ratio since his first year in Boston. The changes to the Boston defense didn't help him much, either. Thanks to a flood of injuries that plagued the club throughout the year, the Sox rarely had their optimal defensive unit on the field behind Beckett.