Glossary

There are a lot of obscure terms uttered throughout the baseball blogosphere regarding statistics and the like. The Glossary page intends to enlighten you to some of these words and their respective definitions. It is meant to be used for quick reference, and certainly not a be-all, end-all resource, so take it for what it is. If there is anything you don’t like or believe to be incorrect, please let us know.

• Replacement Level – expected performance of a typical AAA call-up player, who would ideally “replace” an injured or free agent player. This performance is measured in terms of runs created (offense) and runs saved (defense). Replacement level varies because it is relative to the position’s strength. A replacement level first baseman has higher expectations offensively than a replacement catcher. This concept can also be applied to pitchers. A full 25-man roster of replacement level players will win about 25-30% of the time (roughly 45 wins in a 162 game season).
• WAR (Wins Above Replacement) - how many more (or fewer) expected wins a player contributed to his team. WAR is derived from Runs Above Replacement, which uses other metrics to determine how many runs were contributed or saved compared to a replacement level player at the same position. An expected win is about ten (10) runs. An average starting pitcher or position player who plays most of a season is worth about 2 WAR. While the methods used to measure defensive runs saved are not unanimously agreed upon, batting and pitching is pretty standard.
• BABIP (Batting Average on Balls in Play) - the batting average of a hitter or the batting average of all hitters versus a certain pitcher on swings that make contact. This is higher than a regular batting average because it doesn’t take into account strikeouts. BABIP is often used as a predictor of future performance – if a player or pitcher has an unusually high BABIP that is not in line with league or career averages, it often means that the hitter has been lucky (unlucky for the pitcher) and their BABIP will likely regress towards the mean. If it is very low, the inverse is true. Many players have been falsely praised or scolded based on a given season in which they had lucky or unlucky BABIPs, although many players, essentially the great players and the bad players, can consistently stay at the high or low ends of BABIP, respectively.