SoSH Glossary: wOBA

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wOBA

Weighted on-base average (wOBA) is a rate statistic that aims to measure the total offensive contributions made by a hitter. Rather than treating reaching base regardless of whether it’s done via a walk or hit (like OBP) – or treating a double as if it’s twice as valuable as a single (like SLG) – wOBA values each outcome differently. Each year, the value assigned to each outcome changes slightly based on the league-wide run environment. Finally, weighted on-base average is scaled to league-average OBP, so that the league-average wOBA will equal the league-average OBP.

How Is It Calculated?

 

The goal of wOBA is to give each player a value which accurately reflects the rate at which he produces runs. So, instead of attaching simple, easy-to-remember weights to each offensive event like SLG (“a single is worth 1, a double 2, etc.), wOBA assigns a very particular fraction, one which best expresses the connection between instances of that event by all players, all season long, and the runs scored by all players, all season long. That means that the weights attached to each event will change slightly each year, based on the current run-scoring environment.

What’s the Catch?

The two commonly raised drawbacks are rather minor. The first is that the statistic is not adjusted for park effects, so a hitter who plays for the Colorado Rockies will have a bloated wOBA compared to a San Diego Padre. The second is that this statistic is context-neutral, meaning that it does not account for the game situation when valuing the production of the offensive player, so a home run to lead off the game counts the same as a walk-off home run

Additional Information

wOBA was created by Tom Tango and featured heavily in The Book: Playing the Percentages in Baseball. Tango sought to find an alternative to the increasingly popular OPS, and so he created his own statistic, using linear weights to assign values to each possible outcome.

If you would like to calculate a player’s wOBA yourself, FanGraphs.com has the weights dating all the way back to 1871. Or you could just go to the player’s page on FanGraphs.


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3 COMMENTS

  1. Why is the lack of park adjustment considered minor? Though I’m not well versed in statistics that would seem to be a massive, perhaps fatal, flaw in wOBA that other stats rightfully correct for.

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