Batting Average (AVG):
Divide the number of base hits by the total number of at bats. If Todd Helton has 500 at bats and has 200 hits 
His batting average would be .400 (200/500) 

Slugging Percentage (SLG):
Divide the total number of bases of all base hits by the total number of times at bat
Barry Bonds has 200 total bases and 400 at-bats. Divide 200 by 400 to get his slugging percentage: 200/400=.500 

On-Base Percentage (OBP):
Divide the total number of hits plus Bases on Balls plus hits by Pitch BY at Bats plus Bases on Balls plus hit by Pitch plus Sacrifice Flies In Mo Vaughn's 400 at-bats, he has 150 hits, 60 walks, and has been hit by 25 pitches. He's hit 15 sacrifice flies. So here's the formula to determine his on-base average: (150+60+15)/(400+60+25+15)=225/500=.450


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.

Base On Balls Percentage - (Number of Total Walks (divided by) Number of Plate Appearances)
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. Newer than batting average but nice to use and understand for determining hitters that are "perhaps" more respected or simply have a better "eye."

Home Run Ratio - (Number of Home Runs Hit (divided by) Number of At Bats)
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 at bats that directly result in the player hitting a home run. Newer than batting average but nice to use and understand for determining hitters that are more apt to hit home runs more often than others.

Isolated Power [ISO] - (Total Bases - Hits (divided by) At Bats)
Isolated Power, or extra-bases 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.


Major League Equivalency [MLE] - (Secret Formula)
This is a "secret" 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 a tool for future predictions but rather determines the player's level of performance in the past and adjusts for the difficult level in the big leagues to estimate performance on a current Major League roster.

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.


Plate Appearances [PA] - (At-Bats + 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, 3.1 plate appearances per game are required for batting title eligibility.


Runs Created [RC] - (On Base Percentage + 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.


Strikeout Ratio - (Number of Strikeouts (divided by) Number of At Bats)
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 at bats that directly result in the player striking out. Not one of the nicest hitting statistics to lead the league in each year.


Stolen Base Percentage - (Number of Successful Stolen Bases (divided by) Number of Stolen Base Attempts)
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 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.


Total Base Percentage [TBP] - (Hits + Walks + Hit-By-Pitch) divided by (At Bats + Walks+ Hit-By-Pitch) 
This statistic is 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.

Earned Run Average (ERA):
Multiply the total number of earned runs by nine, and divide the results by the total innings pitched.
Curt Schilling has allowed 100 runs in 300 innings. 
What's his ERA?  Multiply 100x9=900.  Divide  (his innings pitched):  900/300=3.00  That's his ERA 

W-L percentage:
Divide the number of games won by the total number of decisions.
Kevin Brown has a 20-5 record.
Divide his win total (20) by his total number of decisions (25): 20/25=.80 or 80%  

Adjusted Pitching Runs [APR or PR/A] (Innings Pitched divided by 9) x (League ERA - ERA)
An advanced pitching statistic used to measure the number of runs a pitcher prevents from scoring compared to the league's average pitcher in a neutral park in the same amount of innings. This is similar to the ERA+ statistic listed below and acts as a quantitative counterpart.


Earned Run Average Plus [ERA+ or RA] League ERA (divided by) ERA
This statistic uses a league normalized earned run average in the calculation and is meant to measure how well the pitcher prevented runs from scoring relative to the rest of the league. It is a similar to the hitter's PRO statistic and when calculated the decimal is also dropped here.


Game Score - 50 + (3 x Innings Pitched) - 2 x (Hits + Runs + Errors) - Walks + Strikeouts + (+2 divided by each full inning completed beyond the 4th inning)
An advanced pitching statistic developed by Bill James of STATS, Inc used to measure how dominant a pitcher performed in each game he pitched. Often referred to as "Ryanicity" since Nolan Ryan and his multiple no-hitters were amongst the best Game Scores ever recorded until Kerry Wood threw his 20 K's game in 1998. The strikeouts in that game combined with the lack of hits (1) made it better than a perfect game as the statistics rewards dominance (strikes) and lack of hits while penalizing for walks.


Opposing Team's Batting Average - Number Of Allowed Hits (divided by) Number of Outs + Number of Allowed Hits 
Another common statistic in baseball and also quite easy to understand and easy to compute. The primary purpose for this measurement is to gauge the opposing team's batting average when facing this particular pitcher in the game currently being pitched.

Walks And Hits per Innings Pitched [WHIP] (Hits + Walks) divided by Innings Pitched
An extremely popular statistic that is primarily used and discussed with the Fantasy Leagues and Rotisserie Leagues. Developed to measure the approximate numbers of walks and hits a pitcher allows in each inning he pitches then compares the value received to other pitchers to formulate a pitcher's index.


Winning Percentage - Number of Wins (divided by) Number of Decisions 
Another common statistic in baseball and also quite easy to understand and easy to compute. The primary purpose for this measurement is to gauge the percentage of a pitcher's games that are won.


Hold 
This pitching term was created by the people at USA Today and awards a relief pitcher who preserves the lead by not allowing any runs (earned or unearned) and passes it on to another pitcher for a save opportunity.

Save 
A pitcher can earn a save by completing ALL three of the following items:
1. Finishes the game won by his team.
2. Does not receive the win.
3. Meets one of the following three items:
a: Enters the game with a lead of no more than three runs and pitches at least one inning.
b: Enters the game with the tying run either on base, at bat, or on deck.
c: Pitches effectively for at least three innings.

Defensive Average or [DA]
A Defensive Average, or DA, is the rate at which fielders in their respective "zone" turn hit balls into an out. The zone, or area of responsibility, spans the entire field and no section of the playable field is considered beyond the reach of a fielder. The Defensive Average statistics is nice because it is analogous to a fielder's Batting Average Against in that it specifically measures times reached per opportunity.

Fielding Average - (Putouts + Assists) divided by (Putouts + Assists + Errors)
The fielding average, or fielding percentage, defensive statistic is the most common rating system being used in baseball today. It is meant to measure the success rate of fielding opportunities by each player. The official scorer for each game plays a role in this statistic by determining if the hit ball would have required an ordinary amount of effort to turn the play (thereby charging an error to the fielder if they did not turn the play) or an extraordinary amount of effort to turn the play (which does not result in an error charged to the fielder). The downfall to this statistic is that it almost rewards fielders who choose not to attempt a difficult play, thereby avoiding the error, to those that try to turn every hit ball into a possible out.

Fielding Runs [FR]
Fielding Runs is a common term for any statistical treatment of fielding that converts a fielder's performance to runs. Total Baseball uses the most common approach and most easily understood version. Their approach involves weighting the number of putouts, assists, and double plays made by each fielder, and comparing those totals to positional norms of other fielders to arrive at a figure above or below average. Each extra out made, or hit allowed, is worth X runs which leads to the FR figure. Career figures are considered better indicators than individual seasons as normalization is required for better overall averaging of each fielder's statistical performance.

Zone Rating [ZR]
The Zone Rating system is different because the area of responsibility, or zone, for each fielder is considered a "playable" area and does not account for balls hit into "Bermuda Triangles", "No Mans Land" or other impossible to field balls. A fielder that turns a double play is credited with 2 outs in the ZR system as their play on the ball actually resulted in both outs versus Defensive Average which only credits the 1 out. STATS, Inc. books area available at every bookstore and their work is updated on a yearly basis for player comparisons.

Range Factor [RF] - (Putouts + Assists) x 9 divided by Defensive Innings Played
Range Factor simply stated is the number of plays MADE per game at the fielding position. It is better than Fielding Average in several respects: It can be calculated for almost any player this century and it takes into account the fielder's own ability to get to a batted ball - rewarding the more gifted players at each position. Positions can only be successfully compared to the same position on the field when using this statistic and early in the season numbers are often skewed as players chances are not yet normalized.

Fielding Average:
Divide the total number of putouts and assists by the total number of putouts, assists and errors.
Nomar Garciaparra has 250 putouts and 250 assists, while committing only 5 errors.  
His fielding percentage is : (250+250)/(250+250+20)=500/520= .9615

Magic Numbers:
Determine the number of games yet to be played, add one, then subtract the number of games ahead in the loss column of the standings from the closest opponent. So here's Texas' magic number: Games remaining (50) +1=51. 51-7=44. The Rangers' magic number to clinch the AL West is 44.