Glossary Primer

For those new to BaseballHQ.com or who need a quick refresher on the site's most-used terms and benchmarks, here's our quick glossary primer. For a deeper dive on these and other terms, check our Full Glossary.

Batters

xBA (Expected Batting Average) attempts to distill the Batting Average by considering the batter’s speed, power, and distribution of grounders, flies, and line drives. xBA should correlate closely to BA; a variance exceeding 30 points usually portends future change.

bb% (Walk Rate) is a measure of a batter’s plate patience. The best batters will have levels of more than 10%, while the worst will be less than 5%.

Brl% (Barrel rate) A “barrel” is a Statcast metric defined by MLB.com as a well-struck ball where the combination of exit velocity and launch angle generally leads to a minimum .500 batting average and 1.500 slugging percentage. Barrel rate (Brl% in hitter boxes) is simply the number of barrels divided by the number of batted balls for a given hitter.

ct% (Contact Rate) measures a batter’s proficiency in hitting the ball into the field of play; the more often a batter makes contact with the ball, the higher the likelihood he will hit safely. League averages are 79%, with supreme contact hitters above 90% and hackers less than 75%.

Eye (Batting Eye) assesses a batter’s strike-zone judgment by tracking the ratio of walks to strikeouts (bb/k). The best hitters often have Eye ratios greater than 1.00 (more walks than Ks) while those with ratios less than 0.50 are usually plagued by lower BA.

h% (Hit Rate, or Batting Average on Balls in Play, for hitters) is the percentage of balls struck into the field of play that fall for hits. Every hitter establishes his own h% that stabilizes over time; three-year h% levels strongly predict a player’s h% the following year.

HctX (Hard Contact Index) is a combination of ct% and hard-hit ball percentage, compared to overall league levels for that year. A 100 value represents average league power skills; best levels will exceed 130.

G/L/F or GB/LD/FB (Ground balls/Line drives/Fly balls, for hitters) is the percentage of each type of balls hit into the field of play. Increased fly ball percentage for an individual hitter may fortell a rise in power skills; an increase in line drive percentage may indicate a coming batting average increase.

QBaB (Quality of Batted Balls): For batters, greater exit velocity and greater mean launch angle are better. In addition, reduced launch angle variability is correlated with better batted ball results. The Quality of Batted Ball
score (QBaB) assigns A-F grades for exit velocity, launch angle, and launch angle variability based on percentile groupings.

hr/f (Home Run to Fly Ball rate, for hitters) is the percentage of fly balls that a player hits that end up as home runs. Every hitter establishes his own hr/f that stabilizes over time; three-year hr/f strongly predict a player’s hr/f the following year.

PX (Power Index) measures a hitter’s extra-base abilities compared to overall league levels for that year. A 100 value represents average league power skills; the biggest power hitters exceed 150.

Spd (Statistically Scouted Speed) is a skills-based gauge that measures a player’s speed independent of stolen bases. The formula, which dampens power influences and emphasizes factors like infield hits and the player’s body mass, is an index with a midpoint of 100.

SBO (Stolen Base Opportunity Percentage) is a rough approximation of how often a base runner attempts a stolen base, and takes into account how often the manager for that player’s team gives a “green light” to his runners.

BPV (Base Performance Value, for hitters) is a single value used to track a player’s performance trends and predict future performance. BPV encapsulates a hitter’s overall raw skills—batting eye, contact rate, power, and speed—with the best hitters earning a 50 or better. BPX is simply BPV scaled to a league average of 100, such that a BPX of 110 is 10% above average and a BPX of 90 is 10% below league average.

Pitchers

xERA (Expected Earned Run Average) attempts replicate ERA from a skills-dependent perspective, stripping out situation-based factors. xERA should correlate closely to ERA; a variance of more than 1.00 (a run per game) is a strong indicator for future change.

BB% (Walk rate) Measures how many walks a pitcher allows as a percentage of total batters faced.

K% (Strikeout rate) Measures how many strikeouts a pitcher produces as a percentage of total batters faced.

K-BB% (Strikeout minus walk rate) Measures a pitchers’ strikeout rate (K%) minus walk rate (BB%) and is a leading indicator for future performance.

G/L/F or GB/LD/FB (Ground balls/Line drives/Fly balls, for pitchers) is the percentage of each type of balls hit into the field of play. For a pitcher, the ability to keep the ball on the ground (45% and above) can contribute to his statistics exceeding his raw skill level.

hr/f (Home Runs per Fly Ball rate) is the percent of fly balls surrendered by a pitcher that end up being home runs. For pitchers, research has shown that fly balls result in a home run 10% of the time, and that a high hr/f rate in one season is not predictive of a high hr/f the next season. Pitchers with a high hr/f often have an artificially high ERA, and this can be expected to correct itself over time.

hr/9 (Opposition Home Runs per 9 IP) measures how many HR a pitcher allows per game equivalent. The best pitchers will have hr/9 levels of less than 1.0.

H% (Hit Rate, or Batting Average on Balls in Play, for pitchers) is the percentage of balls struck into the field of play that fall for hits. For pitchers, the league average is 30%, and any plus or minus variance of 3% or more can impact the pitcher’s ERA. As a pitcher’s H% corrects back to 30%, his ERA is likely to also move accordingly.

S% (Strand Rate) is the percentage of allowed runners that a pitcher strands. Those with strand rates over 80% will have artificially low ERAs prone to relapse, while levels below 65% will inflate the ERA but with a high probability of regression.

BPV (Base Performance Value, for pitchers) is a single value used to track a pitcher’s performance trends and predict future performance. BPV encapsulates a pitcher’s overall raw skills—power, control, and command—with BPVs of 50 (starters) and 75 (closers) the minimums for long-term success. BPX is simply BPV scaled to a league average of 100, such that a BPX of 110 is 10% above average and a BPX of 90 is 10% below league average.

SwK% (swinging strike rate) measures the percentage of total pitches against which a batter swings and misses, and serves as a useful cross-check on Dom (k/9). League average SwK% is about 8-8.5%, with best rates are over 9.5%

FpK% (first-pitch strike rate) measures the percentage of first-pitch strikes a pitcher throws, and serves as a useful cross-check on Ctl (bb/9). Values below 60% indicate control problems, with best rates at 65% or higher.