BABIP is short for Batting Average on Balls In Play: it's like regular BA, with HRs and K's taken out, and can be calculated for both hitters and pitchers. Surprisingly, it has been shown most pitchers have little control over it, despite a strong correlation to ERA. Once a ball has left the bat and stays in the park, it will be a hit around 30% of the time, regardless of whether you are Randy Johnson (career BABIP .295) or Jamie Moyer (.287).â†µ
A hurler can beat the odds for a bit, getting a freakishly-low BABIP (and resulting ERA) when pitches get hit at the fielders, or suffering a high value because balls fall in. But odds are, it will regress to league average, and take their ERA with it. So you can use extreme values of BABIP as a fairly reliable guide to predict future performance. Here are the top and bottom five, among qualifying starters in 2010:
This isn't to say Livan Hernandez will immediately implode, just confirms what we already knew - that his 1.04 ERA is completely unsustainable. But if you have any of the top five on your fantasy team, now is a good time to sell them, because the odds are their value is only going to decrease. Later in the season, I'll check back in and see how these ten men have done, going forward.