From BR Bullpen
Statistics are very important to baseball, perhaps more than any other sport. Since the game of baseball has a very structured flow to it, the game lends itself to easy record keeping and statistics. This makes comparisons between players on field performance relatively easy, and therefore gives statistics about baseball more importance than in most other sports.
 Development of statistics
The practice of keeping records of the achievements of the players was started in the 19th century by Henry Chadwick. Chadwick devised the predecessors to modern day statistics such as batting average, runs scored, and runs allowed based on his experience of cricket.
Traditionally, statistics like batting average for batters (the number of hits divided by the number of at bats) and earned run average (approximately the number of runs given up by a pitcher per nine innings) have governed the statistical world of baseball. However, the recent advent of sabermetrics has brought about an onslaught of new statistics. These statistics are designed to be a better gauge of player's performance and contributions to his team from year to year.
Comprehensive, historical baseball statistics were difficult for the average fan to access until 1951, when researcher Hy Turkin published "The Complete Encyclopedia of Baseball". In 1969, MacMillan Publishing printed its first Baseball Encyclopedia, using a computer to compile stats for the first time. "Big Mac" became the standard baseball reference until 1988, when Total Baseball was released by Warner Books, using even more sophisticated technology. Interestingly, this work led to the discovery of several players who didn't belong in official record books. Several of these "phantom ballplayers", like Lou Proctor, were expelled from the record books.
 Use of statistics
General managers and baseball scouts study player statistics in order to make decisions on the abilities of players. Managers, catchers and pitchers study statistics of batters on opposing teams to figure out how best to pitch to them and position the players on the field. Managers and batters study opposing pitchers to figure out how best to hit against them. Managers often base their personnel decisions during the game on statistics, such as choosing who to put in the lineup, or which relief pitcher to bring in.
Throughout much of modern baseball, several core statistics have been traditionally used. Batting average, RBIs, and home runs are the most commonly referenced batting statistics. To this day, a player who leads the league in these three statistics is referred to as the "Triple Crown" winner. For pitchers, wins, ERA, and strikeouts are the most often cited traditional statistics. A pitcher that manages to lead the league in these statistics is also referred to as a "Triple Crown" winner.
Some sabermetric statistics have entered the mainstream baseball world. Among statistics that measure a batter's overall performance, On-base plus slugging (OPS) is one of the easiest to calculate. It adds the hitter's on base percentage (number of times reached base—by any means—divided by total plate appearances) to his or her slugging percentage (total bases divided by at bats). Some argue that the OPS formula is flawed and that more weight should be shifted towards OBP (on base percentage).
OPS is also useful when determining a pitcher's level of success. 'Opponent On-base Plus Slugging' (OOPS) is becoming a popular way to evaluating a pitcher's actual performance. When analyzing a pitcher's statistics, some useful categories to consider include K/9IP (strikeouts per nine innings), K/BB (strikeouts per walk), and HR/9. WHIP (walks plus hits per inning pitched) and OOPS (opponent on-base plus slugging).
However, since 2001, more emphasis has been placed on Defense-Independent Pitching Statistics. These statistics, such as Defense-Independent ERA (dERA), attempt to evaluate a pitcher according to those events governed solely by the pitcher's performance, regardless of the strength of the defensive players behind him or her.
Also important are all of the above statistics in certain in-game situations. For example, a certain hitter's ability to hit left-handed pitchers might incline a manager to give him or her more chances to face lefties. Other hitters may have a history of success against a given pitcher (or vice versa), and the manager may use this information to engineer a favorable matchup.
 Commonly used statistics
Most of these terms also apply to softball. Commonly used statistics with their abbreviations are explained here. The explanations below are for quick reference and do not fully or completely define the statistic; for the strict definition, see the corresponding article for each statistic.
 Batting statistics
- 1B - Single - hits on which the batter reached first base safely without the contribution of a fielding error.
- 2B - Double - hits on which the batter reached second base safely without the contribution of a fielding error.
- 3B - Triple - hits on which the batter reached third base safely without the contribution of a fielding error.
- AB - At bat - Batting appearances, not including bases on balls, hit by pitch, sacrifices, interference, or obstruction
- AB/HR At bats per home run - at bats divided by home runs
- BA - Batting average (also abbreviated AVG) - hits divided by at bats
- BB - Base on balls (also called a "walk") - times receiving four balls and advancing to first base
- BB/K - Walk-to-strikeout ratio - number of base on balls divided by number of strikeouts
- XBH - Extra base hits - doubles plus triples plus home runs
- FC - Fielder's choice - times reaching base when a fielder chose to try for an out on another runner
- AO/GO - Ground ball fly ball ratio - number of ground ball outs divided by number of fly ball outs
- GDP or GiDP - Grounded into double play - number of ground balls hit that became double plays
- GS - Grand Slam - a home run with the bases loaded, resulting in four runs scoring, and four RBI credited to the batter.
- H - Hits - times reached base because of a batted, fair ball without error by the defense
- HBP - Hit by pitch - times touched by a pitch and awarded first base as a result
- HR - Home runs - hits on which the batter successfully touched all four bases, without the contribution of a fielding error.
- IBB - Intentional base on balls A base on balls (see BB above) deliberately thrown by the pitcher. Also known as IW (intentional walk).
- K - Strike out - number of times that strike three is taken or swung at and missed, or bunted foul
- LOB - Left on base - number of runners not out nor scored at the end of an inning.
- OBP - On base percentage - times reached base (H + BB + HBP) divided by at bats plus walks plus hit by pitch plus sacrifice flies (AB + BB + HBP + SF).
- OPS - On-base plus slugging - on-base percentage plus slugging average
- PA - Plate appearance - number of completed batting appearances
- RC - Runs created - statistic that attempts to measure how many runs a player has contributed to his team
- RBI - Run batted in - number of runners who scored due to a batters's action, except when batter grounded into double play or reached on an error
- SF - Sacrifice fly - number of fly ball outs which allow another runner to advance on the basepaths or score
- SH - Sacrifice hit - number of sacrifice bunts which allows another runner to advance on the basepaths or score
- SLG - Slugging average - total bases divided by at-bats
- TA - Total average - total bases, plus walks, plus steals, divided by plate appearances plus caught stealing
- TB - Total bases - one for each single, two for each double, three for each triple, and four for each home run
- TOB - Times on base - times reaching base as a result of hits, walks, and hit-by-pitches
 Baserunning statistics
- CS - Caught stealing - times tagged out when attempting to steal
- SB - Stolen base - number of bases advanced other than on batted balls, walks, or hits by pitch
- R - Runs scored - times reached home base legally and safely
 Pitching statistics
- BABIP - Batting average on balls in play - batting average against a pitcher on batted balls ending a plate appearance, excluding home runs
- BB - Base on balls (also called a "walk") - times pitching four balls, allowing the batter-runner to advance to first base
- BB/9 - Base on balls times nine divided by innings pitched (Bases on balls per 9 innings pitched)
- BF - Total batters faced - opponent's total plate appearances
- BK - Balk - number of times pitcher commits an illegal pitching action or other illegal action while in contact with the pitching rubber, thus allowing baserunners to advance
- BS - Blown save - number of times entering the game in a save situation, and being charged the run which ties the game.
- CERA - Component ERA - an estimate of a pitcher's ERA based upon the individual components of his statistical line (K, H, 2B, 3B, HR, BB, HBP)
- CG - Complete game - number of games where player was the only pitcher for his team
- DICE - Defense-Independent Component ERA - an estimate of a pitcher's ERA based upon the defense-independent components of his statistical line (K, HR, BB, HBP)
- ER - Earned run - number of runs that did not occur as a result of errors or passed balls
- ERA - Earned run average - earned runs times innings in a game (usually nine) divided by innings pitched
- G - Games pitched (aka 'Appearances') - number of times a pitcher pitches in a season
- GF - Games finished - number of games pitched where player was the final pitcher for his team
- G/F - Ground ball fly ball ratio - ground balls allowed divided by fly balls allowed
- GS - Starts - number of games pitched where player was the first pitcher for his team
- H/9 - Hits per nine innings - hits allowed times nine divided by innings pitched (also known as H/9IP - Hits allowed per 9 innings pitched)
- H - Hits Allowed - total hits allowed
- HB - Hit batsman - times hit a batter with pitch, allowing runner to advance to first base
- HLD (or H) - Hold - number of games entered in a save situation, left in save situation, recorded at least one out, and not having surrendered the lead
- HR - Home runs allowed - total home runs allowed
- IBB - Intentional base on balls allowed
- IR - Inherited runners - number of runners on base when the pitcher enters the game
- IRA - Inherited runs allowed - number of inherited runners allowed to score
- IP - Innings pitched - number of outs recorded while pitching divided by three
- IP/GS - Average number of innings pitched per game
- K - Strikeout - number of batters who received strike three
- K/9 - Strikeouts per nine innings - strikeouts times nine divided by innings pitched (Strikeouts per 9 innings pitched)
- K/BB - Strikeout-to-walk ratio - number of strikeouts divided by number of base on balls
- L - Loss - number of games where pitcher was pitching while the opposing team took the lead, never lost the lead, and went on to win
- OBA - Opponents batting average - hits allowed divided by at-bats faced
- PIT - Pitches thrown (Pitch count)
- RA - Run average - number of runs allowed times nine divided by innings pitched
- RAA - Runs Against Average - a sabermetric statistic to predict win-percentage.
- SO - Shutout - number of complete games pitched with no runs allowed
- SV - Save - number of games where the pitcher enters a game led by the pitcher's team, finishes the game without surrendering the lead, is not the winning pitcher, and either (a) the lead was three runs or less when the pitcher entered the game; (b) the potential tying run was on base, at bat, or on deck; or (c) the pitcher pitched three or more innings
- W - Win - number of games where pitcher was pitching while his team took the lead and went on to win (also related: winning percentage)
- WP - Wild pitches - charged when a pitch is too high, low, or wide of home plate for the catcher to field, thereby allowing one or more runners to advance or score
 Fielding statistics
- A - Assists - number of outs recorded on a play where a fielder touched the ball, except if such touching is the putout
- DP - Double plays - one for each double play during which the fielder recorded a putout or an assist.
- E - Errors - number of times a fielder fails to make a play he should have made with common effort, and the offense benefits as a result
- FP - Fielding percentage - total plays (chances minus errors) divided by the number of total chances
- INN - Innings - number of innings that a player is at one certain position
- PB - Passed ball - charged to the catcher when the ball is dropped and one or more runners advance
- PO - Putout - number of times the fielder tags, forces, or appeals a runner and he is called out as a result
- RF - Range factor - ([putouts + assists]*9)/innings played. Used to determine the amount of field that the player can cover
- SB - Stolen bases - number of times a runner advanced on the pitch without being thrown out by the catcher
- TC - Total chances - assists plus putouts plus errors
- TP - Triple play - one for each triple play during which the fielder recorded a putout or an assist
 General statistics
- G - Games played - number of games where the player played, in whole or in part
 Further Reading
- Gabriel B. Costa, Michael R. Huber and John T. Saccoman: Understanding Sabermetrics: An Introduction to the Science of Baseball Statistics, McFarland, Jefferson, NC, 2008.
- Curveball (ISBN 0-387-98816-5) - A book on new statistics for Baseball.
- William Darby: Deconstructing Major League Baseball, 1991-2004: How Statistics Illuminate Individual and Team Performances, McFarland, Jefferson, NC, 2006.
- Gary Gillette and Lyle Spatz: "Not Chiseled in Stone... Baseball's Enduring Records and the SABR Era", The Baseball Research Journal, SABR, Volume 40, Number 2 (Fall 2011), pp. 7-11.
- Glenn Guzzo: The New Ballgame: Understanding Baseball Statistics for the Casual Fan, ACTA Sports, Skokie, IL, 2007.
- Bill James: "Stats", in Geoffrey C. Ward and Ken Burns: Baseball: an Illustrated History, Alfred A. Knopf, New York, NY, 1994, pp. 101-103.
- Kevin Reavy and Ryan Spaeder: Incredible Baseball Stats: The Coolest, Strangest Stats and Facts in Baseball History, Sports Publishing LLC, New York, NY, 2016. ISBN 978-1-6132-1894-5
- Alan Schwarz: The Numbers Game: Baseball’s Lifelong Fascination with Statistics St. Martin's Press, New York, NY, 2005.