wOBA: Weighted On-Base Average

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by Dan Bernstein

@dan_bernstein

Boers and Bernstein weekdays 1-6 PM on 670 the Score and 670TheScore.com.
Central to modern baseball analysis is the concept of on-base percentage.
More significant than batting average, OBP (hits, walks and hit-by-pitches divided by plate appearances) has a powerful correlation to offensive success, especially when considering this simple philosophy: a team that makes no outs scores an infinite number of runs.
The problem with OBP is that it treats a walk the same as it does a home run.  Both are plate appearances that resulted in not being out, and that’s it.  We know that the two outcomes are not of equal value, of course, so the easiest thing to do was just add a player’s slugging percentage (total bases divided by at-bats) to it, getting a better sense of total offensive value with On-base Plus Slugging, or OPS.
OPS is nice, but still has obvious holes.  A perfect OBP is 1.000, but a perfect SP is 4.000 (a home run every time up), so a percentage point has differing value for each.  Also, the on-base component is almost twice as important in creating runs.
Statistician Tom Tango (now a Cubs consultant) addressed this by devising Weighted On-Base Average, or wOBA.
His formula found a way of elevating the question from “Did the player get on base?” to “Ok, then, which base?”  A hit is worth more than a walk, a double more than a single, etc., so we have one simple number that gives us a better, truer sense of total offense, giving more weight to the hits that have more run value.
What’s more, it is set up to track to OBP, so we know how to judge it.  .320 is the usual MLB average, .350 is good, .375 is great, .400 is superior, and anything under .300 is awful.
For example, last season’s top five (per fangraphs.com) were Triple Crown winner Miguel Cabrera at .417, Ryan Braun at .413, Mike Trout at .409, Buster Posey at .406, and Andrew McCutchen at .403.
The Cubs’ top offensive player was Alfonso Soriano, ranking 51st at a respectable .350.
The best ever?  No surprise.  Babe Ruth, with a ridiculous career number of .513.
The actual math Tango employed — if you’re interested — is linked here:  http://www.fangraphs.com/library/offense/woba/, but the good news is that we don’t need to be mathematically inclined to appreciate such a useful, reasonable catch-all statistic that measures multiple aspects of hitting a baseball.
Here’s a post about the Cubs from this week: http://www.fangraphs.com/blogs/the-2013-cubs-better-than-we-think/
Dan

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