Baseball Statistics Explained
What every stat means, how it's calculated, and who leads all-time
Baseball has one of the richest statistical traditions in sports. From classic counting stats like home runs and batting average to advanced metrics like OPS and WAR, each number tells a different story. Browse the guides below to understand what each stat means, how it's calculated, and who the all-time leaders are.
BATTING STATS
OPS
On-Base Plus Slugging
A composite batting stat that adds on-base percentage and slugging percentage. One of the most predictive hitting metrics.
Learn more →AVG
Batting Average
The ratio of hits to at-bats. The most traditional measure of a batter's ability to make contact.
Learn more →HR
Home Runs
Hits on which the batter rounds all the bases and scores. The most celebrated offensive achievement in baseball.
Learn more →RBI
Runs Batted In
The number of runs a batter causes to score through their at-bats. A core measure of run production.
Learn more →SLG
Slugging Percentage
Total bases divided by at-bats. Measures a batter's power by weighting extra-base hits more than singles.
Learn more →OBP
On-Base Percentage
How often a batter reaches base per plate appearance. Considered more predictive of run scoring than batting average.
Learn more →SB
Stolen Bases
Times a baserunner successfully advances to the next base without a batted ball. The primary measure of a player's baserunning aggression.
Learn more →BB
Walks (Base on Balls)
Times a batter reaches first base after receiving four balls. A key measure of a hitter's plate discipline and pitch recognition.
Learn more →PITCHING STATS
ERA
Earned Run Average
How many earned runs a pitcher allows per nine innings. The primary measure of a pitcher's effectiveness.
Learn more →WHIP
Walks plus Hits per Inning Pitched
How many baserunners (via walks or hits) a pitcher allows per inning. A precise measure of a pitcher's ability to control the game.
Learn more →Wins
Pitcher Wins
A pitcher is credited with a win when they are the pitcher of record when their team takes a lead they never relinquish.
Learn more →SO
Strikeouts (Pitching)
The number of batters a pitcher retires by strikeout. The premier measure of a pitcher's pure stuff and dominance.
Learn more →SV
Saves
A save is awarded to a relief pitcher who finishes a game for the winning team under specific conditions of closeness.
Learn more →K/9
Strikeouts Per Nine Innings
How many strikeouts a pitcher averages per nine innings pitched. The premier measure of a pitcher's swing-and-miss stuff.
Learn more →BB/9
Walks Per Nine Innings
How many walks a pitcher issues per nine innings. A key measure of command and control.
Learn more →ADVANCED STATS
WAR
Wins Above Replacement
An all-in-one metric estimating how many wins a player contributes above a replacement-level player. The premier advanced statistic.
Learn more →FIP
Fielding Independent Pitching
A pitching metric that isolates what a pitcher directly controls — home runs, walks, and strikeouts — independent of the defense behind them.
Learn more →BABIP
Batting Average on Balls in Play
The rate at which balls put in play by a batter fall for hits. A key indicator of luck and true skill for both hitters and pitchers.
Learn more →wOBA
Weighted On-Base Average
A comprehensive offensive metric that weights each type of hit and walk by its actual run value. One of the best single-number measures of offensive production.
Learn more →PIV
Player Impact Value
Baseball Data Hub's proprietary offensive metric measuring how much value a player creates above league average, adjusted for durability and era.
Learn more →FREQUENTLY ASKED QUESTIONS
What is ERA in baseball?
ERA (Earned Run Average) measures how many earned runs a pitcher allows per nine innings pitched. It is calculated as (Earned Runs × 9) ÷ Innings Pitched. A lower ERA indicates better pitching performance. See the ERA explanation page for full details and all-time leaders.
What is OPS in baseball?
OPS (On-Base Plus Slugging) combines on-base percentage and slugging percentage into a single offensive metric. An OPS above .900 is considered excellent at the major league level. Barry Bonds holds the all-time career OPS record at 1.051. See the OPS explanation page.
What is WAR in baseball?
WAR (Wins Above Replacement) is an all-in-one metric estimating how many wins a player contributes compared to a replacement-level player. A 5 WAR season is All-Star quality; 8+ is MVP territory. Babe Ruth holds the career record. See the WAR explanation page.
What is the difference between AVG, OBP, and SLG?
Batting Average (AVG) measures how often a batter gets a hit per at-bat. On-Base Percentage (OBP) includes walks and hit-by-pitches, measuring how often a batter reaches base. Slugging Percentage (SLG) weights hits by their total bases, rewarding extra-base hits. Together they form the OPS metric.