Baseball statistics
From Academic Kids

As with many sports, and perhaps even more so, statistics are very important to baseball. A seemingly intrinsic part of the game is the keeping of statistics on the achievements of the players.
The practice was started by Henry Chadwick in the 19th century who devised the concepts of batting average and earned run average based on his experience of cricket. Statistics have been kept for the Major Leagues since their creation.
General managers and baseball scouts study player statistics to decide what players to try to get for their team. Managers, catchers and pitchers study statistics of batters on opposing teams to figure out how best to pitch to them and position the players. Managers and batters study opposing pitchers to figure out how best to hit 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.
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 advent of sabermetrics brought an onslaught of new statistics that better gauge a player's performance and contributions to his team from year to year.
Some sabermetrics have entered the mainstream baseball statistic world. Onbase plus slugging (OPS) is a somewhat complicated formula that gauges a hitter's performance better than batting average. It combines the hitter's on base percentage ([hits + walks + number of times hit by pitches] divided by [number of times at bat + walks + number of times hit by a pitch + number of sacrifice flies]) with their slugging percentage (total bases divided by at bats). Walks plus hits per inning pitched (or WHIP) gives a good representation of a pitcher's abilities; it is calculated exactly as its name suggests.
Also important are all of those statistics in certain ingame situations. For example, a certain hitter's ability to hit lefthanded pitchers might cause his manager to give him 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 favourable matchup.
Comprehensive, historical baseball statistics were difficult for the average fan to access until 1951, when researcher Hy Turkin published the "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. (This led to discovery, and expulsion, of several players who didn't belong in the record books  "phantom ballplayers", like Lou Proctor.)
Contents 
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 batters only reached first base safely
 2B  Double  hits on which batters only reached second base safely
 3B  Triple  hits on which batters only reached third base safely
 AB  At bat  Batting appearances, not including bases on balls, hit by pitch, sacrifices, interference, or obstruction
 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/SO  Walktostrikeout ratio  number of base on balls divided by number of strikeouts
 EBH  Extra base hit (Sometimes EB or XBH)  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
 G/F  Ground ball fly ball ratio  number of ground balls divided by number of fly balls
 GIDP  Ground into Double play  number of ground balls hit that became double plays
 H  Hit  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 run  hits on which the batter successfully touched all four bases, scoring a run and batting in between one and four runs (a home run with four runs batted in – i.e. bases loaded – is a Grand Slam).
 OBP  On base percentage  times reached base divided by plate appearances
 OPS  Onbase plus slugging  onbase percentage plus slugging percentage, a very good measure of a hitter's ability
 PA  Plate appearance  number of completed batting appearances resulting in atbats, bases on balls, hitbypitches, or sacrifice flies
 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 score
 SH  Sacrifice hit  number of bunt outs which allow another runner to advance
 SLG  Slugging percentage  total bases divided by atbats
 SO  Strike out (also abbreviated K)  number of times that strike three is taken or swung at and missed, or bunted foul
 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 a base or when picked off
 SB  Stolen base  number of bases advanced other than on batted balls, walks, or hits by pitch.
 R  Run  times reached home base legally and safely
Pitching statistics
 AVG  Opponents batting average  hits allowed divided by atbats faced
 BB  Base on balls (also called a "walk")  times pitching four balls, allowing runner to advance to first base
 BS  Blown save  number of times entering the game in a save situation, and being charged the run which ties the game.
 CG  Complete game  number of games where player was the only pitcher for his team
 DIPS  Defense independent pitching statistics  a measure of a pitcher's effectiveness that doesn't include balls in play
 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
 GIR  Games in relief  number of games pitched where player was not the starting pitcher for his team
 GF  Games finished  number of games pitched where player was the final pitcher for his team
 GP  Games pitched  number of games in which the player pitched
 G/F  Ground ball fly ball ratio  ground balls allowed divided by fly balls allowed
 GS  Games started  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
 HA  Hits Allowed  total hits allowed
 HBP  Hit by pitch  times hit a batter with pitch, allowing runner to advance to first base
 HLD  Hold  number of games entered in a save situation, left in save situation, recorded at least one out, and not having surrendered the lead
 IBB  Intentional base on balls
 IRA  Inherited runs allowed  number of runners allowed to score who were on base when pitcher enters the game
 IP  Innings pitched  number of outs recorded while pitching divided by three
 R/9  Runs per nine innings  number of runs allowed times nine divided by innings pitched
 SHO  Shutout  number of complete games having allowed zero runs
 SO  Strikeout (also abbreviated K)  number of batters who received strike three
 SO/9  Strikeouts per nine innings  strikeouts times nine divided by innings pitched
 SO/BB  Strikeouttowalk ratio  number of strikeouts divided by number of base on balls
 SV  Save  number of close games finished where the pitcher's team won
 TBF  Total batters faced  opponent's total plate appearances
 W  Win  number of games where pitcher was pitching while his team took the lead and went on to win (also related: winning percentage)
 L  Loss  number of games where pitcher was pitching while the opposing team took the lead and went on to win
 W+S  Relief wins plus saves  wins plus saves
 WHIP  Walks plus hits per inning pitched  bases on balls plus hits divided by innings pitched
 W/9  Walks per nine innings  bases on balls times nine divided by innings pitched
See also
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  errors divided by total chances
 PB  Passed ball  number of times the catcher allows a runner to advance but should have been able to prevent it with ordinary effort
 PO  Putout  number of times the fielder tags, forces, or appeals a runner and he is called out as a result
 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.
 WP  Wild pitch  number of times a runner advances due to a pitcher's poorly thrown pitch.
General statistics
 G  Games played  number of games where the player played, in whole or in part
 WW  "Wasn't Watching"  used by nonofficial scorekeepers when their attention is distracted from the game  said to have been invented by Phil Rizzuto
See also
 Triple Crown in Major League Baseball
 MLB Most Valuable Player Award winners
 Cy Young Award winners
 MLB Rookie of the Year Award winners
 Gold Glove Award winners
Other terminology
References
 Official Baseball Rules, Section 10  Scoring (http://www.mlb.com/NASApp/mlb/mlb/baseball_basics/mlb_basics_official_scorer.jsp) from http://www.mlb.com
 Find statistics for all of major league history at http://www.BaseballReference.com/
 The Baseball Cube (http://www.thebaseballcube.com) Statistical Database for Major League, Minor League and College baseball.
 Retrosheet (http://retrosheet.org) Historical boxscore information
 Baseball Almanac (http://www.baseballalmanac.com)
 The Society for American Baseball Research (http://www.sabr.org)