Adjusted Production [APRO or PRO] 
(On Base Percentage divided by League OBP) + (Slugging Average divided by League SA) 1
The adjusted production statistic is a park and league adjusted version of on base plus slugging percentage. It is specifically used and created by Total Baseball for comparison of players from different eras in different parks. This is an advanced statistic which requires the complete understanding of on base percentage, slugging average and a park adjustment factor. Total Baseball has adjusted OBP and SA for the player's home park and League OBP and League SA are the league average for each statistic respectively. As in OPS, the decimal point is dropped when APRO in seen or used. It is vulnerable to conjecture and inaccuracy since the "league averages" are difficult to calculate at a given time.

Batting Average or [AVG or BA] 
Number of Hits (divided by) Number of At Bats
This is certainly the most common statistic in baseball and the most understood, even outside of the game and by those that do not know the game. (The terms you're batting a thousand or you're batting zero are used often.) It has been historically used as the benchmark for hitters since the late 1800's making it historically rich, easy to understand, easy to compute and almost everyone knows what a .300 hitter is. One of the only disadvantages is the batting average statistic does not take into account walks or extrabase hits, however, other statistics do.

Base On Balls Percentage 
Number of Total Walks (divided by) Number of Plate Appearances
This is another common statistic in baseball and also quite easy to understand and easy to compute. The primary purpose for this offensive measurement is to gauge the percentage of a batter's appearance at the plate that directly result in the player being walked. It is newer than batting average but nice to use and understand for determining hitters that are "perhaps" more respected or simply have a better "eye." It does not differentiate from an intentional walk or an earned walk. 
Home Run Ratio 
Number of Home Runs Hit (divided by) Number of At Bats
This also is a very common statistic in baseball and also quite easy to understand and easy to compute. The primary purpose for this offensive measurement is to gauge the percentage of a batter's at bats that directly result in the player hitting a home run. It is a different gauge than batting average but nice to use and understand for determining hitters that are more apt to hit home runs more often than others. Home run hitters ofer do not have high batting averages. 
Isolated Power [ISO] 
Total Bases  Hits (divided by) At Bats
Isolated Power, or extrabases per at bats, was also invented by Branch Rickey and All Roth during the 1950's. On Base Percentage measured for the manager how often a player reaches base while the isolated power showed them how often those bases reached were extra base hits  beyond a single. The total bases here was calculated by awarding 0 for a single, 1 for a double, 2 for a triple and 3 for a home run. This is a calculation that favors teams that play "big ball" and not "small ball". 
Major League Equivalency [MLE] 
Proprietary Formula
This is a "proprietary" formula used and developed exclusive by Bill James of STATS, Inc. which is used to determine what a Minor League player would have hit had he been a player in the Major Leagues. It is not used as a tool for future predictions but rather determines the player's level of performance in the past and adjusts for the difficulty level in the big leagues to estimate performance on a current Major League roster. It borders on voodoo and is subject to conjecture and misunderstanding. 
On Base Percentage [OBP or OBA] 
(Hits + Walks + HitByPitch) divided by (At Bats + Walks+ HitByPitch + Sac Flys)
The On Base Percentage statistic was originally created by Branch Rickey and Allan Roth in the 1950's as a means to measure the percentage of times a player reaches any base. Some leagues and clubs now include dropped third strikes, errors (since a fast runner can "force" them), fielder's choice plays and interference as valid on base qualifiers. It did not originally include the sacrifice fly denomination but when it was officially adapted in 1984 it appeared using the formula written above. It is easily one of the most important statistics and it is specifically written with managers in mind. 
On Base Plus Slugging [OPS] 
On Base Percentage + Slugging Average
This is not a true statistic by definition but it is often used as an index for rating an overall player's performance and production versus his fellow players. The formula above requires the use and understanding of two others [OBP and SA], also on this page, and when seen in text appears without the decimal point. 
Official Plate Appearances [PA]  Official At Bat [OAB] 
Hits + Reaching Base By Error + An Out (excluding sacrifices) + Fielde's Choice
Official plate appearances are as follows: the batter reaches first base on a hit, the batter reaches first base on an error, the batter is called out for any reason other than as part of a sacrifice, or there is a fielder's choice. See Batting Average. 
Plate Appearances [PA] 
AtBats + Bases on Balls + Hit By Pitcher + Sacrifice Hits + Sacrifice Flies + Times Reached on Defensive Interference
Plate appearances have long sparked controversy as it is a factor used to determine the yearly batting champion. Currently, a minimum of 3.1 plate appearances per game are required for batting title eligibility. This is NOT the same as Official plate appearances. 
Runs Created [RC] 
On Base Percentage x Total Bases
This statistic was originally created by Bill James to measure a player's total offensive production. By combining the two statistical (OBP and TB which are listed on this page) results you can determine that desired production. Bill James describes it by saying scoring runs consists of two actions: First  getting on base or creating baserunners (which is on base percentage) and Second  the advancing of those runners around the bases (which is total bases). A superb stat that creates a great index for offensive ratings. 
Runs Created Per 25 [RC25] 
Runs Created (divided by) Number of Outs x 25
This statistic was also created by Bill James and uses the results of the runs created formula listed above. You then divide by the number of outs the player actually made and multiply it by 25. The figure is an estimate of how many runs a team created. 
Slugging Average [SA or SLG] 
Number of (Singles + [2 x Doubles] +[ 3 x Triples] + [4 x Home Runs]) divided by At Bats
A players Slugging Average, or Slugging Percentage, is directly defined as total bases per at bat. To calculate a player's total bases you award a 1 for a single, a 2 for a double, a 3 for a triple, and a 4 for a home run then add them all together. Divide that by the total number of at bats a player has and you can easily determine the overall number of bases a player generally touches during his at bats. 
Strikeout Ratio 
Number of Strikeouts (divided by) Number of At Bats
Another common statistic in baseball and also quite easy to understand. Heavy strikeouts hurt the team in that they give NO opportunity for a productive out, as in advancing the runner on an out. The primary purpose for this offensive measurement is to gauge the percentage of a batter's at bats that directly result in the player striking out. Leading the league each year in a given statistic is usually a good thing. This one is a dubious honor to lead the league in each year. 
Stolen Base Percentage 
Number of Successful Stolen Bases (divided by) Number of Stolen Base Attempts
An excellent offensive statistic in baseball; these are bonus bases and often caused forced errors often generating runs. The primary purpose for this offensive measurement is to gauge the percentage of a base runners attempted steals that directly result in the player successfully stealing the base. 
Stolen Base Runs [SBR] 
(.3 x Stolen Bases)  (.6 x Caught Stealing)
This is another very good Total Baseball statistic aimed at quantifying base stealing. Numerous statistical studies done by Total Baseball have shown that the break even success rate for steals (the rate at which an attempt to steal is neither helping nor hurting the team in terms of total runs scored) is about 67%. Each successful steal adds approximately .3 runs to a team's total runs scored which is much less than often believed. Therefore, the statistic is meant to estimate the impact of base stealers, which, other than the elite base stealers, rarely amounts to more than a few runs per year for each team. However, this is a flawed statistic in that errors which are often caused by base stealers do NOT figure into the production of runs. 
Total Base Percentage [TBP] 
(Hits + Walks + HitByPitch) divided by (At Bats + Walks+ HitByPitch)
This statistic is is outdated and no longer used as a newer, improved version was adopted in 1984 by Major League Baseball and listed above. See On Base Percentage. This worked the in the same respect however it failed to account for a player's sacrifice flys hit during a game. Virtually all leagues are using the newer formula. 
Total Bases [TB] 
Number of (Singles + [2 x Doubles] +[ 3 x Triples] + [4 x Home Runs])
When calculating batting average, every hit simply counts as one. Total bases places a "weight" on each base hit and according to The Baseball Dictionary "computes his worth as a batter." 