Sabermetrics: wOBA

For my second sabermetrics post, I thought I would talk about a complex sabermetric that combines many simpler, more widely understood statistics: wOBA, or weighted On-Base Average. An improvement from the tradition triple slash-line, the goal of wOBA is to assess a player’s “offensive value” in measuring how capable a hitter is of moving himself and his teammates around the bases to generate runs.

Before I attempt to explain wOBA itself, however, it is important to understand the simpler stats that factor into wOBA. Batting average measures how often a player gets a hit, but does not factor in walks. On-base percentage measures how often a player reaches base, regardless of how. Slugging percentage weighs how many bases a hitter covers per hit, but does not include walks. wOBA attempts to combine all of these stats into a number that takes into account not only how many bases are covered per hit, but the odds of a hit also removing another play from a base, so it takes walks into account.

The formula itself uses average weights of how valuable a type of hit is to the overall possibility of said type of hit generating a score in order to correctly factor in all ways of reaching base (walks, hits, homers, getting hit by pitch) to calculate what a player contributes offensively.

With that in mind, I’ll let FanGraphs present the wOBA formula:

wOBA = (0.690×uBB + 0.722×HBP + 0.888×1B + 1.271×2B + 1.616×3B +
2.101×HR) / (AB + BB – IBB + SF + HBP)

**FanGraphs specifies that the weights in this formula are for the 2013 season, and change slightly each year.**

It is important to remember that wOBA does not take into account disparities in ballparks (some ballparks are considered “hitters ballparks,” meaning it is easier to hit a home run, for example, based on the outfield configuration/ length of the outfield than other ballparks) or in-game context (this includes runners on base or the score of the game during the player’s at-bat).

In general, an average wOBA is about .320, with anything above that being about average to excellent; excellent is .400. There are a number of MLB players currently with season wOBA averages significantly above even the excellent mark. They are all in close contention,  none of their names are surprising, and some have absolutely fabulous haircuts. Joey Votto (.429), Bryce Harper (.427) and Aaron Judge/Paul Goldschmidt (.426) are the current 2017 wOBA leaders. These players, then, are exemplary in scoring production solely from the plate–stolen bases and other on-base events do not factor into wOBA, so these guys are some true productive sluggers.

Cue Bryce Harper hair flip.

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