Saber 101: Weighted On-Base Average (wOBA)

What if I told you that there is a statistic that measures everything a player can do offensively, would you be interested? Additionally, what if that statistic came in a scale that you already know what is good and what is bad? Oh, and it included stolen bases and caught stealing and it is easily converted to a tangible run value?

I know, it sounds complicated, and there is a decent-sized formula that comes along with it. But, would it soften the blow if I told you it was inspired by a Sesame Street song?

Okay, so the statistic itself wasn't inspired by Sesame Street song above, but that is where Tom Tango got the acronym wOBA (pronounced just how it is in the video).

Ladies and gentleman, I bring you Weighted On-Base Average (wOBA), the last offensive statistic you need to use after the jump...

What is wOBA?

To begin, we should note wOBA is on the same scale as On-Base Percentage, which has become 'mainstream' enough of a statistic that most people are aware that around .335 is league average, .370 is very good and above .400 is elite. Conversely, below .320 is bad and if you're below .300 you're probably employed by the Kansas City Royals.

In not-so-simplistic terms, wOBA measures the total run value of all the singles, doubles, triples, homers, non-intentional walks, hit-by-pitches and the times a player reaches base on errors accumulated by a player. These run values -- or Linear Weights -- aren't just random numbers, either.

Linear Weights are a concept way before our time and founded by Pete Palmer and George Lindsey in the 1960s -- Sabermetrics stretches well before Bill James coined the term in the early 1980s -- and Tango and company have carried the torch and applied it in creating wOBA.

Tango's research into the history of the game has found, on average, how many runs each of the above events is worth. For instance, the home run is worth 1.95 runs because there are multiple types of homers -- solo shots and homers with men on base. Update:  Tom Tango corrected me that the HR is about 1.70 runs more than an out.

After all of the calcuations are done, the value is converted to the same scale as OBP, giving us an easy way to compare what players did at the plate. Update There was clarification made by Tom Tango saying that all these run values are multiplied by a constant to get it on the OBP scale -- for instance, the HR is multiplied by close to 2.

For a more detailed explanation, Tango wrote one at Inside The Book.

Why can't I use OPS?

Well, you can use OPS if you'd like. However, the research done by many analysts have shown that getting on base is more important than slugging in terms of run creation. Obviously, you want as much of both on-base and slugging as you can find in a player, but those are few and far between. If you're forced to choose between the high OBP guy or a high-SLG guy, the high OBP guy will create more runs than the slugger. So, wOBA paints the view of a player's offensive value that OPS was thought to.

Flaws in the system

There really aren't "flaws" per-se, but what wOBA measures is context neutral. That is, it doesn't care how many people were on base when Cabrera homered, just that he homered. It also doesn't care whether he hit a walk-off grand slam or a squeaker of a solo shot down the left field line in the bottom of the first inning. However, over the course of a specific sect of time, you will get a very accurate picture of the number of runs Cabrera (or any player) added to their teams offense.

However, the wOBA that you see on the player pages of Fangraphs are not park-adjusted. They do this behind-the-scenes as they calculate their Wins Above Replacement totals, but the raw wOBA's are unadjusted. Ideally, this would be fixed, but it's not a huge problem.

There are some who prefer to use Equivalent Average (EqA), but those people primarily write for  Baseball Prospectus -- the same site that houses EqA. Colin Wyers (before joining the B-Pro team) found virtually no difference between the two in terms of capturing what a player does offensively -- the only difference between the two is that EqA is scaled to look like batting average instead of OBP like wOBA. If you prefer that, then hey, no problem. I prefer wOBA because it's on a site I don't have to pay for.

Why you should use it

  • Accurately weights the ability to get on base with slugging ability? Check.
  • Can easily be turned into a run value? Check.
  • Can be turned into a Runs Above Average number with ease? Check.
  • Is readily available (along with UZR) on one website? Check.
  • Is easily added in with UZR to form another piece of the puzzle that a player's entire value? Check.

And it's named after a Sesame Street song for cryin' out loud. What more do you need that Grover singing in your mind when you look up a players offensive contributions? Nothing.

Fangraphs now now added wRC+ which is just like OPS+ that many people quote from Baseball Reference.This is how a player rates versus league average on a 100-scale where 100 is exactly average. Due to this addition, there shouldn't be another reason to use OPS again.

Resources

As always, Fangraphs is where the cool kids are hanging around at. Alex Remington's explanation of wOBA was a great backbone for this Saber 101 series. Thanks Alex, where ever you are!

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