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BABIP or Batting Average on Balls In Play is the percentage of all balls put in play by the batter that resulted in a base hit. This excludes HRs. The commonly-used equation to find a player's BABIP is:


Some analysts include reached base on error (RBOE) in the numerator, while others exclude SF from the denominator.

The fielders behind the pitcher, as is the park, are also partly responsible for how high or low a pitcher's BABIP is.

BABIP can be considered to have a direct relationship to Defensive Efficiency Record or DER. DER is the number of outs made by fielders per ball in play (excluding home runs). So, DER plus BABIP could equal 1, depending on the definition being used for BABIP.

Sample Size[edit]

The reliability of any metric will increase as its sample size will increase. For a pitcher, seasonal BABIP is a largely unreliable measure of his skill. In order for this metric to do a good job in measuring his skill, you need several seasons worth of data.

This leads to the myth that a pitcher's skill in hit prevention is mostly the product of luck: we can't see year-to-year consistency in the metric as the noise overwhelms the signal. But, as we increase the number of years, the signal can finally match the noise.

For hitters, a seasonal BABIP is a bit more indicative in explaining his skill in getting hits: the year-to-year consistency is stronger for batters than for pitchers.

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