BABIP Batting Average for Balls in Play
A hitter's BABIP describes the proportion of balls in play that result in hits. The average BABIP is usually around .300 at the major league level, but the league average can be as high as .340 in some of the lower minor leagues. Although BABIP is a repeatable skill to some degree, an unusually high or low BABIP is usually an indicator of good or bad luck.
BABIP = (H-HR)/(AB-HR-SO)
BB% Walks per Plate Appearance
Walk rate describes the proportion of plate appearances (or batters faced, from a pitcher's perspective) that result in walk.
BB% = BB / PA
BsRA9 Base Runs Allowed per 9 Innings
Base Runs (BsR) is a technique for run estimation that actually models the run scoring environment and is accurate in a wide range of contexts. The formula can be described this way:
Runs = Baserunners * The Proportion of Baserunners Who Score + Home Runs
BsRA9 is an application of this technique estimator for pitchers. The result estimates a pitcher's expected runs allowed per 9 innings.
Click here for more information about BsRA9 (Base Runs allowed per 9 innings).
BsRA% Base Runs Allowed Percentage
BsRA% describes the proportion of expected runs allowed relative (BsRA9) to actual runs allowed. A BsRA% near 100 indicates a high correlation between expected runs allowed and actual runs allowed, but a BsRA% below 90 or above 110 suggests a pitcher allowed fewer or more runs than expected due to situational factors.
BsRA% = BsRA / RA
FIP Fielding Independent Pitching
FIP is an estimate of a pitcher's ERA that considers all things that fielders cannot influence; strikeouts, walks, and home runs. Most pitchers' ability to influence balls in play is relatively weak, so FIP or DIPS are more useful estimates of a pitcher's ability than ERA. The formula includes a league-specific factor that ranges from 3.0 to 3.5 depending on the league and year. HBP data is not available for all pitchers in our database, so HBP may be estimaed in some cases.
FIP = ((HR*13 + (BB+HBP) * 3 - SO * 2) / IP ) + ~3.2
GB% Groundball Percentage
Groundball percentage describes the proportion of batted balls that are hit on the ground. These rates are fairly stable for both pitchers and hitters.
GB% = GB / Batted Balls
GPA Gross Production Average
GPA was developed as an alternative to OPS because on base percentage should be weighted more heavily than slugging percentage. GPA is also scaled in a way that makes it easy to interpret. Like batting average, a GPA over .300 is good while a GPA under .250 is not good.
GPA = ((OBP * 1.8) + SLG) / 4
HR/Air Home Runs per Airborne Batted Ball
HR/Air describes the percentage of line drives and outfield fly balls that result in a home run. Pitchers have limited control over this rate, and extremely low or high values are typically influenced by the pitching context.
HR/Air = HR / (FB + LD)
ISOP Isolated Power
Isolated Power is a pure measure of a hitter's power. Only doubles, triples, and home runs contribute to a batter's ISOP. Most productive batters' ISOP is somewhere between .150 and .200, but elite sluggers can produce ISOP of .300 and greater.
ISOP = SLG - BA
K% Strikeouts per Plate Appearance
Strikeout rate describes the proportion of plate appearances (or batters faced, from a pitcher's perspective) that result in strikeout.
K% = K / PA
LD% Line Drive Percentage
Line drive percentage describes the proportion of batted balls that are categorized as line drives.
LD% = LD / Batted Balls
LOB% Left On Base Percentage
Left On base Percentage describes the proportion of baserunners that a pitcher allows to score. The mean strand rate is typically around 75%. Although a very high or low strand rate may be indicative of a lucky or unlucky pitcher, there is evidence that this may be a repeatable skill to some degree.
OBP On Base Percentage
OBP is a common statistic that describes how frequently a batter reaches base.
OBP = (H + BB + HBP) / (AB + BB + HBP + SF)
OPS On Base Plus Slugging
OPS is a convenient way to estimate a batter's total offensive production; it is simply OBP plus SLG. OPS is often criticized for undervaluing OBP. Although there are more accurate ways to evaluate a player's or team's offesnive production, OPS is easy to calculate and is highly correlated with run production.
OPS = OBP + SLG
RA9 Runs Allowed per 9 Innings
RA9 describes how many runs a pitcher would allow over nine innings. It is calculated the same way ERA is, but with all runs instead of earned runs. The determination of errors and what makes a run an earned run is somewhat subjective, so some individuals prefer RA9 over ERA as an estimate of how valuable a pitcher was over a period of time.
RA9 = (R / IP) * 9
RC Runs Created
Runs Created estimates the number of runs a batter contributed to his team's offense. Bill James created several versions of runs created, and we use a basic version that includes stolen bases.
Runs created per 27 outs, or RC/27, is an estimate of how many runs a lineup of one player would score over a full game (27 outs).
RC = ( (H + BB - CS) * (TB + (0.55 * SB) ) ) / (AB + BB)
SLG Slugging Percentage
A hitter's slugging percentage describes the total bases achieved per an at bat. It is the most commonly-used estimate for a batter's power and is the "S" in OPS . It is not, however, a pure measure of a batter's power because it is highly correlated with batting average (see ISOP).
SLG = TB / AB
TBF Total Batters Faced
Total Batters Faced is a count of batters that recorded a plate appearance against a pitcher. It is the denominator in the BB% and K% statistics for pitcher.
wOBA Weighted On Base Average
This represents a player's offensive value by scaling linear weights in a way that resembles OBP. In general, a major league wOBA around .340 is average and a wOBA of .400 is very good. wOBA is featured prominently in The Book.
wOBA = (0.72 BB + 0.75 HBP + 0.90 1B + 0.92 RBOE + 1.24 2B + 1.56 3B + 1.95 HR) / PA