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Weighted on-base average gives measure of offensive success

Baseball is filled with cliches. And like all cliches, some are excessively corny — Gopher ball? High cheese? Really? — while others have a touch of truth to them. You don't want to make the first or third out at third base, and yes, batters do tend to struggle against same-handed pitchers.

What about this cliche: "A walk is as good as a hit." Well, is it? If you have read Money­ball, then you're probably inclined to say yes. But as a certified stathead and nerd, I'm here to tell you the correct answer is no.

Don't get me wrong, walks are excellent. As they stress in Moneyball, the most important thing a batter can do is not make an out. Teams get only 27 outs in one game, so batters extend the game and improve their team's chances of winning simply by reaching base through whatever means possible. In this context, a walk is as good as a hit.

But walks do have their limitations. In the large picture, singles are more valuable than walks because they have the ability to advance runners. You can't drive in a runner from third with a walk (unless the bases are loaded), and you can't advance a runner from first to third with one, either.

Really, this is common sense. Singles are more valuable than walks, doubles are more valuable than singles, triples more valuable than doubles, and home runs are more valuable than all of them. All baseball fans should know this intuitively. Once you accept this premise, though, you're essentially admitting that none of baseball's traditional offensive stats properly capture value.

Batting average counts every hit as the same, and it ignores walks completely. On-base percentage includes walks, but it counts them as equally important as a home run or any other hit. And slugging percentage ignores walks and arbitrarily decides that a home run is four times as valuable as a single.

That's not to say these statistics are worthless. Each tells something important about a hitter. My point is simply that none of them capture everything.

On-base plus slugging, or OPS, attempts to solve this problem by adding on-base percentage and slugging percentage. While it's a noble effort, it's not entirely accurate. By adding OBP to SLG, singles are twice as valuable as walks and doubles three times as valuable as walks. Are 50 singles as valuable as 100 walks? This seems like a big exaggeration.

In general, OPS undervalues walks and overvalues home runs and doubles, giving a large boost to power hitters. It's a good shorthand statistic and is more comprehensive than any of the other traditional stats, but we still haven't answered the question: How do we properly value offense?

Let me introduce you to the statistic "wOBA." Weighted on-base average looks at all aspects of hitting, weighing each in proportion with their actual value. These values were determined by empirically answering the following question: On average, how much do singles, walks, etc., increase a team's chances of scoring? Walks are given a boost (singles are only around one-third more valuable than walks), and home runs are bumped down from four times as valuable as a single to just less than 2.5 times.

Weighted on-base average is presented on the same scale as on-base percentage, so it should be intuitive to determine if a player has a good or bad wOBA. A .380 OBP is excellent, so a .380 wOBA is also great. If a .316 OBP is league average, then a .316 wOBA is also league average. And if a player has a wOBA so low that it'd make a bad batting average, then you know that hitter has issues.

You can find wOBA at FanGraphs.com, and I'll use it occasionally in columns. It's not a mainstream statistic — although it was highlighted on Baseball Tonight this past week — but it's a short, quick way to accurately sum up a player's offensive portfolio.

If you're still attached to batting average, on-base percentage and slugging percentage, that's fine, but realize that those stats give you only pieces to the puzzle. Casey Kotchman hasn't been the Rays' second most valuable hitter this year simply because of his batting average; he has been valuable because he has hit for a high average, drawn lots of walks and displayed some pop as well.

Those puzzle pieces each have meaning and value, but how do we put them together correctly? For that, we need wOBA.

Steve Slowinski is the editor-in-chief of DRaysBay.com, a blog on the Tampa Bay Rays that specializes in analysis and statistics.

Weighted on-base average gives measure of offensive success 08/27/11 [Last modified: Saturday, August 27, 2011 9:16pm]
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