Explanation of Statistics

Batting Statistics

• AB--At Bat.  Official times at bat which count in the batting average.  Plate appearances which do not count as an AB are: base on balls, hit by pitch, sacrifice bunt, sacrifice fly, and catcher's interference.
• R--Runs. Runs scored by the player.  A courtesy runner who eventually scores receives this statistic for himself, and not for the person for whom he is running.
• H--Hits.  Number of times the player hits safely to get on base, i.e., a single, double, triple, or home run.  It does not count as a hit when a player gets on base by an error, a fielder's choice, a base on balls, hit by pitch, catcher's interference, or reaching first safely on a dropped third strike. 
• RBI--Runs Batted In.  The number of runs which are a result of the player's plate appearance.  Besides those counted by a hit, the batter may also receive an RBI if the bases are loaded and he is awarded first base because of a base on balls, hit by pitch or catcher's interference.  A batter may also receive an RBI on an error if there are less than two outs, and the runner would have scored on an errorless play (in the scorer's judgment).
• 2B, 3B, HR--Doubles, Triples, Home Runs.  The number of each kind of hit the batter received.  Note that sometimes a batter may reach an extra base on an error or a throw to make a play at another base; in such cases, the scorer may award the number of bases that the player would have received had there been errorless play or had the throw come in toward the batter-runner.
• BB--Base on Balls.  The number of times the player was issued a walk, including intentional walks.  Such plate appearances do not count toward AB's and therefore do not figure into the batting average.
• K--Strike Out.  The number of times the player struck out, including called strike outs and bunting foul on a third strike.  This number also includes times a player stikes out, but reaches first safely on a dropped third strike.
• SB--Stolen Base.  The number of times the player safely steals a base, including double steals.
• CS--Caught Stealing.  The number of times the player was out while stealing a base.  This does not count on pickoffs when the runner is out diving back to the base, but it does count if the runner makes any attempt to run away from the pickoff.
• HP--Hit by Pitch.  The number of times the player is awarded first base because the ball hit him or any piece of his clothing.  If a player is hit within the strike zone, it is not counted as a hit by pitch and the player is not awarded first base (usually it is counted as a foul ball).
• SAC--Sacrifice Bunt.  The number of times a batter bunts to advance a previous runner.  It still counts as a SAC if the batter reaches first on an error.  Such plate appearances do not count toward AB's and therefore do not figure into the batting average.
• SF -- Sacrifice Fly.  The number of times a batter hit a fly ball to a fielder and a runner scored after the ball was caught.  It still counts as a SF if the fielder drops the ball for an error.  Such plate appearances do not count toward AB's and therefore do not figure into the batting average.
• CI -- Catcher Interference.  The number of times a batter is awarded first base because of catcher interference, usually when the catcher brushes the bat during a swing.  Technically, "obstruction" is the term used when the defense interferes with play ("interference" is usually reserved for a batter/runner who interferes with the fielders).  However, the term "catcher interference" is firmly entrenched in the statistical lore.
• PA -- Plate appearances.  The number of times a player completes a turn at the plate; this is the sum of AB, BB, HP, SAC, SF, and CI. 
• AVG -- Batting Average.  The average number of times a player gets a hit for every official at-bat (AB).  Mathematically, this is H / AB (hits divided by at-bats).  The batting average is usually expressed without the decimal, i.e., "He's batting three forty-five! That's terrific!"  This is where the term "batting a thousand" comes from (to indicate perfection).
• OBA -- On-Base Average.  The average number of times a player gets on base, not including errors.  This is like the on-base average but includes walks and sacrifice flies (don't ask me why, it just does).  Mathematically, this is (H+BB)/(AB+BB+SF) [or, the number of hits plus walks divided by the number of at-bats plus walks plus sacrifice flies].  This number is usually greater than the batting average.
• SLG -- Slugging Average.  This is a synthetic statistic meant to indicate how often a batter gets extra bases on his hits.  It is calculated like the batting average, but an additional "hit" is added for each extra base.  For example, if a batter had 3 hits in 10 at-bats (0.300 avg), and one of them was a double, then his SLG would be 0.400.  If instead the batter had a home run and 2 singles, then his SLG would be 0.600.  Mathematically, this is (H + 2B + 3B + 3B + HR + HR + HR)/AB.

Fielding Statistics

• A'st -- Assists.  The number of times a fielder assists in putting out a batter/runner.  For instance, a shortstop would get an assist for a grounder hit to him which he fields and throws to first base for the out.  Multiple assists in one play (say, in a rundown) only count once, although a fielder may get both an assist and a put-out in a double play.  A player may get an assist on a play even if the fielder receiving a throw commits an error (say, dropping a ball at first).
• PO -- Put-outs.  The number of times a fielder is responsible for putting out the batter/runner by catching the ball, stepping on the base for a force out or appeal, or by tagging the runner.  In addition, a strikeout is credited to the catcher (don't worry, the pitcher gets his own statistic for strikeouts) unless he drops a third strike and has to throw to first base.  Typically, the first baseman and the catcher get the most put-outs in any given game.
• Err -- Errors.  The number of errors committed by a fielder.  An error is defined as a muffed play or throw that would normally have been accomplished through ordinary effort (scorer's judgment).  These are some of the hardest plays to score.  Things that may indicate against an error include field conditions (a bad hop or slick grass), weather conditions (sun in the eyes or wind blowing the ball around), or any play that would be considered extra-ordinary if accomplished.  Slow reactions and mental errors are not generally counted as errors.
• Fld% -- Fielding Percentage.  This statistic indicates how well a fielder handles the ball.  It is the ratio of times he has successfully handled the ball in a putout compared to the total number of times he handled the ball (including errors).  Mathematically this is (Assists + PO) / (Assists + PO + Err).

Pitching Statistics

• IP -- Innings Pitched.  Number of innings the pitcher was official pitcher.  Partial innings are determined by number of outs; 1/3 of an inning for 1 out, 2/3 for 2 outs, etc.  In this spreadsheet, this is expressed as 0.3 and 0.7 respectively (often in newspapers and other boxscores fractional innings are shown as 0.1 and 0.2).  Technically, a pitcher could pitch for more than one inning, but if he fails to get an out before being relieved, then only 1 inning is credited.
• H -- Hits. Number of hits that batters got off of the pitcher.
• R -- Runs. Number of runs scored against the pitcher.  A batter can get on base by pitcher A, who is then relieved by pitcher B, and then later score a run, and it will generally be credited to pitcher A.
• ER -- Earned Runs. The number of runs that would have been scored had there been no errors or passed balls.  This would exclude runs that are scored by runners who get on base due to an error, or who score after an error prolongs an inning.  This is a subjective exercise, usually done by reconstructing the innings as if no errors had occured.
• BB -- Bases on Balls. Number of walks issued by the pitcher, excluding intentional walks.
• SO -- Strike Outs. Number strikeouts issued by the pitcher, including dropped third-strikes.
• HB -- Hit Batsmen. Number of batters hit by the pitcher (where the batter is awarded first base).
• ERA -- Earned Run Average. The average number of earned runs given up by the pitcher in a complete game.  Since high school games last 7 innings, the average is calculated by (ER * 7) / IP [in the major leagues they naturally multiply by 9].
• K/inn -- Strike outs per inning.  The average number of strike outs issued by the pitcher per inning.
• W-L -- Won-Loss Record.  The number of wins and losses credited to the pitcher.