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This sabermetric glossary is reprinted in its entirety from the 2008 Baseball Forecaster. Note that some formulas defined here are not part of the content used on this site.
Abbreviations and Beginning Concepts
Avg:Batting average (see also BA)
BA: Batting average (see also Avg)
BABIP: Batting average on balls-in-play (see Hit rate)
Base Performance Indicator(BPI): A statistical formula that measures an isolated aspect of a player's situation-independent raw skill or a gauge that helps capture the effects that random chance has on skill. Although there are many such formulas, there are only a few that we are referring to when the term is used in this book. For batters, the skills BPIs are linear weighted power index (PX), speed score index (SX), walk rate (bb%), contact rate (ct%), batting eye (Eye), ground ball/line drive/fly ball ratios (G/L/F), home run to fly ball rate (hr/f) and expected batting average (xBA). Random chance is measured with hit rate on balls in play (H%). For pitchers, our BPIs are control (bb/9), dominance (k/9), command (k/bb), opposition on base avg (OOB), ground/line/fly ratios (G/L/F) and expected ERA (xERA). Random chance is measured with hit rate (H%), strand rate (S%) and home run to fly ball ratio (hr/f).
Batting Average (BA, or Avg): A grand old nugget that has long outgrown its usefulness. We revere .300 hitting superstars and scoff at .250 hitters, yet the difference between the two is 1 hit every 20 ABs. This 1 hit every five games is not nearly the wide variance that exists in our perceptions of what it means to be a .300 or .250 hitter. BA is a poor evaluator of baseball performance in that it neglects the offensive value of the base on balls and assumes that all hits are created equal.
bb%: Walk rate (hitters)
bb/9: Opposition walks per 9 IP
BF/Gm: Batters faced per game
BPI: Base performance indicator
BPV: Base performance value
Sabermetrics, Fanalytics and Advanced Concepts
Batting:(AB – K) Pitching:((IP x 2.82)) + H – K
The total number of batted balls that are hit fair, both hits and outs. An analysis of how these balls are hit – on the ground, in the air, hits, outs, etc. – can provide analytical insight, from player skill levels to the impact of luck on statistical output.
Base Performance Value(BPV): A single value that describes a player's overall raw skill level. This is more useful than traditional statistical gauges to track player performance trends and project future statistical output. The BPV formula combines and weights several BPIs.
Batting BPV: ((Walk rate - 5) x 2) + ((Contact rate - 75) x 4) + ((Power Index - 80) x 0.8) + ((Speed Index - 80) x 0.3)
This formula combines the individual raw skills of batting eye, contact rate, power and speed. BENCHMARKS: The best hitters will have a BPV of 50 or greater.
Pitching BPV: ((Dominance Rate - 5.0) x 18) + ((4.0 - Walk rate) x 27) + (Ground ball rate as whole number - 40)
This formula combines the individual raw skills of dominance, control and the ability to keep the ball on the ground, all characteristics that are unaffected by most external team factors. In tandem with a pitcher's strand rate, it provides a complete picture of the elements that contribute to a pitcher's ERA, and therefore serves as an accurate tool to project likely changes in ERA. BENCHMARKS: A BPV of 50 is the minimum level required for long-term success. The elite of the bullpen aces will have BPV's in excess of 100 and it is rare for these stoppers to enjoy long term success with consistent levels under 75.
Batters faced per game (Craig Wright)
((IP x 2.82) + H + BB) / G
A measure of pitcher usage and one of the leading indicators for potential pitcher burnout.(See Usage Warning Flags in the Forecaster's Toolbox.)
Batting average on balls in play (Voros McCracken)
Batting BABIP: (H—HR) / (AB – HR - K)
Pitching BABIP: (H—HR) / ((IP x 2.82) + H - K - HR)
Also called Hit rate (H%). The percent of balls hit into the field of play that fall for hits.See Forecaster's Toolbox for a complete discussion. BENCHMARK: The league average H% is 30%, which is also the level that individual pitching performances will regress to on a year to year basis. Any +/- variance of 3% or more can affect a pitcher's ERA. Batters tend to regress to their own historical three-year mean level.
Batting eye (Eye)
(Walks / Strikeouts)
A measure of a player's strike zone judgment, the raw ability to distinguish between balls and strikes. BENCHMARKS: The best hitters have eye ratios over 1.00 (indicating more walks than strikeouts) and are the most likely to be among a league's .300 hitters. Ratios less than 0.50 represent batters who likely also have lower BA's. (See Forecaster's Toolbox for more.)