MLB Stats Glossary

Number of singles.
Number of doubles.
Number of triples.
Number of at bats.
The percentage of pitches thrown / seen in a count favorable to the player. Defined for pitchers as 0-1, 0-2, 1-2 and 2-2 counts. For hitters it is 1-0, 2-0, 3-0 and 3-1 counts.
Batting average.
Stands for Batting Average on Balls in Play. Balls in play include anything that is hit into the field of play, so strikeouts, walks, and home runs are excluded. (Learn More)
Stands for batting value. It is determined by taking the player’s park-adjusted wOBA and subtracting away the league average wOBA, and then dividing that by 1.15 and multiplying by the number of plate appearances the batter has had.
The number of unintentional walks, expressed as a percentage. (Learn More)
Number of batters faced.
The reverse of Ahd.
The number of batted balls.
The percentage of pitches swung at, that are contacted.
The percentage of pitches swung at, where contact is made.
The percentage of pitches thrown / seen in a count deemed even. Defined as 0-0, 1-1, 2-1 and 3-2 counts.
The percentage of batted balls classified as a fly ball. (Learn More)
FIP stands for Fielding Independent Pitching, and xFIP stands for Expected Fielding Independent Pitching. While FIP and xFIP are not perfect in terms of measuring the performance of a pitcher, most would agree they do a better job representing the pitcher’s true ability than ERA. (Learn More)
The percentage of batted balls classified as a ground ball. (Learn More)
Number of times grounded into a double play.
The number of hits.
The number of hit batters.
The number of home runs allowed or hit.
HR/FB represents the percent of fly balls a pitcher allows that are home runs. (Learn More)
The percentage of fly balls and line drives that go for a home run.
The percentage of batted balls classified as an infield fly. (Learn More)
The number of innings pitched.
ISO stands for Isolated Power. When talking about ‘power’ in a hitting context, we are talking about extra-base hits – doubles, triples, and home runs. (Learn More)
The percentage of batters faced / plate appearances that resulted in a strikeout. (Learn More)
The percentage of plate appearances ending in a called strikeout.
The percentage of strikeouts resulting from a swing and a miss (pitcher) or the percentage of plate appearances ending in a swinging strikeout (batter).
The percentage of batted balls classified as a line drive. (Learn More)
The average leverage index for all plate appearances by the pitcher / hitter.
Stands for Leverage Index and is a quantification of how important a specific play is within the context of the game as a whole. (Learn More)
Stands for left on base percentage. (Learn More)
The percentage of batters faced / plate appearances that resulted in either an unintentional walk or hit batter.
On Base Percentage.
The percentage of pitches swung at outside the strike zone, that were made contact with.
OPS and OPS+ are statistics used to evaluate offensive performance. OPS simply stands for On Base Plus Slugging, while OPS+ is a scaled version of that same idea. (Learn More)
The percentage of pitches thrown outside the strike zone, that were swung at.
The percentage of pitches thrown outside the strike zone, taken for a called strike.
Number of plate appearances.
Stands for plate appearance value. It is used to give credit to the hitter for the difference between average and replacement level for those that wish to use a WAR-style calculation. The difference is set to 20 runs per 600 PAs.
The percentage of fly balls hit to the batter’s pull side.
The number of pitches thrown.
Plate discipline isn’t one stat but rather a collection of stats, each of which tells a slightly different story. Analyzing the various plate discipline stats for a given hitter can reveal strengths and weaknesses, highlight the batter’s gameplan, and even reveal what kinds of pitchers may give him trouble. (Learn More)
Stands for position value. It gives credit for the position that the player plays, but not his quality of play there. That is, this is not about how well a player plays defense, merely where a player plays defense. The values per full season (defined as 5,850 defensive PAs [150 games x 39 PAs per game]) are: +12.5 for catcher, +7.5 for shortstop, +2.5 for second base, third base and center field, -7.5 for left and right field, -12.5 for first base and -17.5 for designated hitter.
Total pitches seen divided by plate appearances.
Quality of contact is a measure of how hard a batter is hitting the ball. (Learn More)
Runs above average.
The percentage of balls in play (i.e. not including home runs), that result in the batter reaching base, either via hit or error.
Stands for run expectancy based on 24 base-out states. (Learn More)
Number of times reaching base via error.
Stands for run value per 600 PAs. It is batV divided by PA multiplied by 600. 600 PAs is considered the bench mark for a full season.
Number of sacrifice bunts.
Stands for Skill-Interactive Earned Run Average. As baseball statistics have developed, it has become clear that traditional ERA does not do a great job of identifying the true skill level of a pitcher. Therefore, a variety of other options have emerged and SIERA has come to be respected as one of the most valuable. (Learn More)
Slugging Percentage.
The number of strike outs.
The percentage of pitches thrown that result in a strike or batted ball.
The percentage of pitches seen, swung at.
The percentage of pitches, swung at and missed.
Stands for Ultimate Base Running. Traditionally, base running has only been quantified by stolen bases and caught stealing. With UBR, however, base running can be given a run value, helping highlight which players add (or subtract) value through their running. (Learn More)
Stands for Ultimate Zone Rating and gives us a way to attach a run value to a player’s defensive abilities.(Learn More)
Win expectancy is the odds of each team winning at any given point in the game. (Learn More)
wOBA or weighted on base average is a statistic developed by and used with the permission of Tom Tango. In a nutshell, wOBA uses linear weights on certain batting events to come up with a metric that is scaled onto an OBP scale. (Learn More)
wOBA* divided by the league’s average wOBA.
This is wOBA, but corrected for the parks the batter has played in that season.
WPA stands for Win Probability Added and identifies how much an individual player is helping or hurting his team’s pursuit of winning games. (Learn More)
Weighted Runs Above Average is an offensive baseball statistic, abbreviated as wRAA. This statistic allows baseball fans to compare a player’s offensive contribution to that of an average hitter. (Learn More)
wRC stands for Weighted Runs Created. These stats are based on an earlier stat simply called Runs Created, which was developed by Bill James. The Runs Created version was typically used to assess how many runs a team would be expected to score, but it was also used occasionally to evaluate players. wRC and wRC+ improve on this earlier version by adding weights to specific outcomes in order to more fairly value performance.(Learn More)
The expected number of home runs allowed or hit based on the park factors and the distribution of batted balls.
The expected number of innings pitched, it is expected outs from the xRA calulations divided by 3 .
The expectd number of runs allowed, from the xRA calculations.
Stands for expected Run Average. xRA assigns run and out values to events under a pitcher’s control and then constructs a run average using expected runs divided by expected outs multipled by 27, the same scale as the more common ERA or RA.
Like wOBA+. xRA+ is equal to the player’s xRA subtracted from league’s xRA and then divided by the league’s xRA. That is then added to one and then multiplied by 100. As a formula it is: ( ( ( league xRA – player xRA ) / league xRA ) + 1 ) * 100.
The percentage of pitches swung at in the strike zone, that were made contact with.
The percentage of pitches with locations recorded landing within the typically called strike zone as defined by pitch F/X. The dimensions of the typically called strike zone vary.
The percentage of pitches thrown in the strike zone, and taken for a called ball.
The percentage of pitches thrown in the strike zone, that were swung at.