In baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

, wOBA (or weighted on-base average) is a statistic, based on linear weights, designed to measure a player's overall offensive contributions per plate appearance. It is formed from taking the observed run values of various offensive events, dividing by a player's plate appearances, and scaling the result to be on the same scale as on-base percentage. Unlike statistics like OPS

On-base plus slugging

On-base plus slugging is a sabermetric baseball statistic calculated as the sum of a player's on-base percentage and slugging percentage. The ability of a player to both get on base and to hit for power, two important hitting skills, are represented. An OPS of .900 or higher in Major League...

, wOBA attempts to assign the proper value for each type of hitting event. It was created by Tom Tango

Tom Tango

Tom Tango and "TangoTiger" are aliases used online by a well-respected expert in baseball sabermetrics and ice hockey statistical analysis. He runs the Tango on Baseball sabermetrics website and is also a contributor to ESPN's baseball blog TMI .In 2006, Tango's book The Book: Playing the...

 and his coauthors for The Book: Playing the Percentages in Baseball.

Usage

In 2008, sabermetrics

Sabermetrics

Sabermetrics is the specialized analysis of baseball through objective, empirical evidence, specifically baseball statistics that measure in-game activity. The term is derived from the acronym SABR, which stands for the Society for American Baseball Research...

 website FanGraphs

Fangraphs

FanGraphs.com is a website run by Fangraphs Inc., located in Arlington, Virginia, and created and owned by David Appelman that provides statistics for every player in Major League Baseball history....

 began listing the current and historical wOBA for all players in Major League Baseball

Major League Baseball

Major League Baseball is the highest level of professional baseball in the United States and Canada, consisting of teams that play in the National League and the American League...

. It forms the basis of the offensive component of their Wins above replacement (WAR) metric. Sites such as The Hardball Times

The Hardball Times

is a website which publishes news, original comments and statistical analysis of baseball each week Monday through Friday, in addition to the Hardball Times Annual book which features essays by leading sabermetric personalities. The website features the slogan "Baseball. Insight...

 have studied wOBA and found it to perform comparably to or better than other similar tools (OPS, Runs created

Runs created

Runs created is a baseball statistic invented by Bill James to estimate the number of runs a hitter contributes to his team.-Purpose:James explains in his book, The Bill James Historical Baseball Abstract, why he believes runs created is an essential thing to measure:With regard to an offensive...

, etc.) used in sabermetrics to estimate runs. The Book uses wOBA in numerous studies to test the validity of many aspects of baseball conventional wisdom.

Formula

The formula, as it originally appeared in The Book, is



where:

• NIBB = Non-intentional bases on balls
  Base on balls
  A base on balls is credited to a batter and against a pitcher in baseball statistics when a batter receives four pitches that the umpire calls balls. It is better known as a walk. The base on balls is defined in Section 2.00 of baseball's Official Rules, and further detail is given in 6.08...
  
  
• HBP = Hit by pitch
  Hit by pitch
  In baseball, hit by pitch , or hit batsman , is a batter or his equipment being hit in some part of his body by a pitch from the pitcher.-Official rule:...
  
  
• 1B = Single
  Single (baseball)
  In baseball, a single is the most common type of base hit, accomplished through the act of a batter safely reaching first base by hitting a fair ball and getting to first base before a fielder puts him out...
  
  
• RBOE = Reached base on error
  Error (baseball)
  In baseball statistics, an error is the act, in the judgment of the official scorer, of a fielder misplaying a ball in a manner that allows a batter or baserunner to reach one or more additional bases, when such an advance would have been prevented given ordinary effort by the fielder.The term ...
  
  
• 2B = Double
  Double (baseball)
  In baseball, a double is the act of a batter striking the pitched ball and safely reaching second base without being called out by the umpire, without the benefit of a fielder's misplay or another runner being put out on a fielder's choice....
  
  
• 3B = Triple
  Triple (baseball)
  In baseball, a triple is the act of a batter safely reaching third base after hitting the ball, with neither the benefit of a fielder's misplay nor another runner being put out on a fielder's choice....
  
  
• HR = Home run
  Home run
  In baseball, a home run is scored when the ball is hit in such a way that the batter is able to reach home safely in one play without any errors being committed by the defensive team in the process...
  
  
• PA = Plate appearance
  Plate appearance
  In baseball statistics, a player is credited with a plate appearance each time he completes a turn batting. A player completes a turn batting when: He strikes out or is declared out before reaching first base; or He reaches first base safely or is awarded first base ; or He hits a fair ball which...