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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...

Star-divide

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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Saber 101: Ultimate Zone Rating

Jan 2010 by Mike Rogers - 19 comments

Comments

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Thanks for the explanation!

Could you explain how you convert wOBA into a run value or RAR?

by Dberg on Jan 19, 2010 4:54 PM EST reply actions  

Yeah, I can, but not at the moment. I will later tonight.

My old blog is Tigers By The Numbers.

Now I write at Bless You Boys.

Like music? See what I'm listening to at my Last.fm account.

by Mike Rogers on Jan 19, 2010 5:00 PM EST up reply actions  

How to convert wOBA into wRAA on Fangraphs

Basically, this is the formula to convert wOBA to a runs above average number:

player wOBa – league wOBA / 1.15 * PA

So, the 2009 MLB wOBA was .329. Let’s roll with a .350 wOBA for Player A:

(.350-.329)/1.15*600

I used 600 PA’s because 700 PA’s is considered 100% playing time and 600 PA’s is about what we’d expect a full time player to get in a season as he’s getting days off and whatnot.

So equate that formula and we get:

.021/1.15*600
0.01826*600
=10.96

So, a .350 wOBA in this formula, stretched over 600 PA’s in 2009 with a league average wOBA of .329 would produce 10.96 Runs Above Average — essentially 11.

Now, the 1.15 modifier is what puts the number on an OBP scale. That .15 part of it changes from year-to-year to get to the league average OBP as league wOBA = league OBP.

If you want that runs total to be above replacement, you’re adding in 22*.85=18.7 runs to make it replacement level. We multiply by .85 because this example is over 600 PA’s which is about 85% playing time.

Does this make sense?

My old blog is Tigers By The Numbers.

Now I write at Bless You Boys.

Like music? See what I'm listening to at my Last.fm account.

by Mike Rogers on Jan 20, 2010 2:40 AM EST up reply actions  

I heart wOBA

It’s like, my favorite and stuff. Excellent work, Mike.

by ChrisDTX on Jan 19, 2010 5:17 PM EST reply actions  

Total Average?

Does anyone remember total average from Tom Boswell in the 80s? I loved it because it showed the true value of Kirk Gibson. He often finished in the top 5 in TA.

"I have seen the future, and it is much like the present, only longer" - Dan Quisenberry

by 3strikes on Jan 19, 2010 6:35 PM EST via mobile reply actions  

Wonderful

This was probably the advanced metric I looked at the least, largely because while I could understand how to compare players with it, I did not fully understand everything that went into it. I will definitely being paying more attention to wOBA from now on.

by baum on Jan 19, 2010 8:29 PM EST reply actions  

is this to me?

My old blog is Tigers By The Numbers.

Now I write at Bless You Boys.

Like music? See what I'm listening to at my Last.fm account.

by Mike Rogers on Jan 20, 2010 2:27 AM EST up reply actions  

Yeah I saw that. And pointed out an error. Whoops.

My old blog is Tigers By The Numbers.

Now I write at Bless You Boys.

Like music? See what I'm listening to at my Last.fm account.

by Mike Rogers on Jan 20, 2010 3:15 PM EST up reply actions  

Thank you guys!

Alex Remington here. I really appreciate the shoutouts — thanks for reading!

http://www.chop-n-change.com

by alexwithclass on Jan 24, 2010 5:59 PM EST reply actions  

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