In baseball, wOBA (/'woʊbə/, or weighted onbase average)^{[1]} is a statistic, based on linear weights,^{[2]} 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 onbase percentage. Unlike statistics like OPS, wOBA attempts to assign the proper value for each type of hitting event. It was created by Tom Tango and his coauthors for The Book: Playing the Percentages in Baseball.^{[3]}
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Usage
In 2008, sabermetrics website FanGraphs began listing the current and historical wOBA for all players in Major League Baseball.^{[4]} It forms the basis of the offensive component of their wins above replacement (WAR) metric. Sites such as The Hardball Times have studied wOBA and found it to perform comparably to or better than other similar tools (OPS, RC, etc.) used in sabermetrics to estimate runs.^{[5]}^{[6]} The Book uses wOBA in numerous studies to test the validity of many aspects of baseball conventional wisdom.
The benefit of wOBA compared to other offensive value statistics is that it values not just whether the runner reached base but how.^{[7]}^{[8]} Events like home runs, walks, singles, etc. are given their own weight (or coefficient) within the linear formula. The weighting is based on the increase in expected runs for the event type as compared to an out. The coefficients change each season^{[9]} based upon how often each event occurs.
Because the coefficients are derived from expected run value, we can use wOBA to estimate a few more things about a player's production and baseball as a whole. When using the formula (shown below), the numerator side on its own will give us an estimate of how many runs a player is worth to his team. Similarly, a team's wOBA is a good estimator of team runs scored, and deviations from predicted runs scored indicate a combination of situational hitting and base running.^{[10]}
2019 Formula
Per Fangraphs, the formula for wOBA in the 2019 season was:^{[9]}
where:
 NIBB = Nonintentional bases on balls
 HBP = Hit by pitch
 1B = Single
 2B = Double
 3B = Triple
 HR = Home run
—————
 AB = at bat
 BB = Base on balls
 IBB = Intentional base on balls
 SF = sacrifice flies
 HBP = Hit by pitch
2018 Formula
The formula for the 2018 season was:^{[9]}
 NIBB = Nonintentional bases on balls
 HBP = Hit by pitch
 1B = Single
 2B = Double
 3B = Triple
 HR = Home run
—————
 AB = at bat
 BB = Base on balls
 IBB = Intentional base on balls
 SF = sacrifice flies
 HBP = Hit by pitch
Ranges for elite, very good, etc.
The following table serves as an aggregate summary of various wOBA scales available online.^{[10]}^{[11]}
Classification  Range 

Elite  .400 and Above 
Very Good  .371 to .399 
Good  .321 to .370 
Average  .320 
Bad  .291 to .320 
Very Bad  .290 and below 
Original Formula
The formula below appeared in The Book.^{[12]}
where:
 NIBB = Nonintentional bases on balls
 HBP = Hit by pitch
 1B = Single
 RBOE = Reached base on error
 2B = Double
 3B = Triple
 HR = Home run
 PA = Plate appearance
Citations
 ^ "The Language Of Fangraphs  FanGraphs Baseball". Retrieved 20181207.
 ^ "Linear Weights  FanGraphs Sabermetrics Library". www.fangraphs.com.
 ^ "wOBA  Weighted On Base Average". www.insidethebook.com.
 ^ "The Joy of wOBA  FanGraphs Baseball". www.fangraphs.com.
 ^ "The great run estimator shootout (part 1)  The Hardball Times". www.fangraphs.com.
 ^ "The great run estimator shootout (part 2)  The Hardball Times". www.fangraphs.com.
 ^ "What is a Weighted Onbase Average (wOBA)?  Glossary". Major League Baseball. Retrieved 20181109.
 ^ "wOBA  FanGraphs Sabermetrics Library". www.fangraphs.com. Retrieved 20181109.
 ^ ^{a} ^{b} ^{c} "Guts!  FanGraphs Baseball". Retrieved 20181109.
 ^ ^{a} ^{b} Rogers, Mike (20100119). "Saber 101: Weighted OnBase Average (wOBA)". Bless You Boys. Retrieved 20181207.
 ^ "The Beginner's Guide To Deriving wOBA  FanGraphs Sabermetrics Library". Retrieved 20181207.
 ^ Tango, Tom M. The book : playing the percentages in baseball. Lichtman, Mitchel G., Dolphin, Andrew E. [Place of publication not identified]. ISBN 9781494260170. OCLC 919473395.
References
 Tom Tango, Mitchel Lichtman, and Andrew Dolphin. The Book: Playing the Percentages in Baseball. Washington, D.C.: Potomac Books, 2007. ISBN 1597971294.