In baseball, wOBA (/'woʊbə/, or weighted on-base 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 on-base 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]
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, Runs created, 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 how the runner reached base, not just if he reached base.[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 year,[9] and are based on how often each event occurs in Major League Baseball over the course of a season.
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 = Non-intentional 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]
where:
- NIBB = Non-intentional 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, as it originally appeared in The Book, is
where:
- NIBB = Non-intentional 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 2018-12-07.
- ^ "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 On-base Average (wOBA)? | Glossary". Major League Baseball. Retrieved 2018-11-09.
- ^ "wOBA | FanGraphs Sabermetrics Library". www.fangraphs.com. Retrieved 2018-11-09.
- ^ a b c "Guts! | FanGraphs Baseball". Retrieved 2018-11-09.
- ^ a b Rogers, Mike (2010-01-19). "Saber 101: Weighted On-Base Average (wOBA)". Bless You Boys. Retrieved 2018-12-07.
- ^ "The Beginner's Guide To Deriving wOBA | FanGraphs Sabermetrics Library". Retrieved 2018-12-07.
References
- Tom Tango, Mitchel Lichtman, and Andrew Dolphin. The Book: Playing the Percentages in Baseball. Washington, D.C.: Potomac Books, 2007. ISBN 1-59797-129-4.