Sabermetric Sunday: wOBA

Jun 14, 2016; New York City, NY, USA; Pittsburgh Pirates left fielder Starling Marte (6) hits a two-run home run against the New York Mets during the eighth inning at Citi Field. Mandatory Credit: Adam Hunger-USA TODAY Sports
Jun 14, 2016; New York City, NY, USA; Pittsburgh Pirates left fielder Starling Marte (6) hits a two-run home run against the New York Mets during the eighth inning at Citi Field. Mandatory Credit: Adam Hunger-USA TODAY Sports /

As I continue my sabermetric Sunday series here at Rum Bunter today we take a look at another offensive stat: wOBA.

Today is a very good day for this article. Why? Well, that is because this past week on Twitter Dave and I have gotten into multiple arguments with people on Twitter about rather OPS is a good stat to evaluate hitters on or not.

In case you were wondering, OPS is not a good stat to evaluate hitters on. OPS is influenced too much by slugging percentage to be a reliable stat. On average, one point of on-base percentage is 1.8 times more valuable than one point of slugging percentage. Yet, slugging percentage carries more weight than on-base percentage does in OPS. That alone makes OPS a bad stat.

Furthermore, OPS fails to take the two best stats to evaluate hitters on into consideration. Those two stats are wRC+, which I discussed last Sunday, and wOBA which I will breakdown today. So, here we go!

Weighted on-base percentage, or simply wOBA, is arguably the best stat to use when evaluating hitters. wOBA is a stat that attempts to credit, or discredit, a hitter based on the value of each outcome at the plate. So with wOBA a single is weighted differently than drawing a walk, and a strikeout is weighted differently than a sacrifice fly.

The reason wOBA does this is to avoid treating each way of reaching base, or each way of making an out, equally. Because not all hits, nor are all outs, created equally. This is one of the reasons I like wOBA so much, because it credits/discredits a hitter based on each individual outcome instead of evaluating them equally.

Look at last night’s game as an example. In the top of the fourth inning the Pirates loaded the bases with no one out. Catcher Erik Kratz stepped to the plate and simply had to hit a ground ball or a fly ball to drive in a run. Instead, Kratz struck out and no run scored.

Erik Kratz’s batting average, on-base percentage, and OPS all were affected the same by this strike out as they would have been by a RBI ground out. However, Kratz’s wOBA was not. wOBA penalized Kratz more for striking out in this at bat than it would have had he put the ball in play and brought home a run.

In my opinion, hitters should be penalized more for failing to make productive outs when they have the chance to do so. Another example from last night came when Jordy Mercer doubled to lead off the third inning, but Josh Harrison failed to move him up. Harrison grounded out to shortstop, keeping Mercer at second base. Now this did not hurt the Pirates and Andrew McCutchen would end up singling Mercer home, but Harrison was penalized more for this than he would have been had he moved the runner up.

As FanGraphs Sabermetric Library points out, wOBA combines all the different aspects of hitting and weights each one accordingly. There is no stat that better captures the offensive value of a hitter with more accuracy or comprehension than wOBA. This is why I am such a huge wOBA fan and why I believe everyone should use it when evaluating hitters.

Next: Pirates Prospects: An Interview With Will Craig

So, how is wOBA calculated? Well let’s talk about that next! The formula for calculating wOBA may seem complicated, but once you break it down it really is not that complicated at all. The formula for calculating wOBA is as follows:

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

You can see how wOBA weighs each outcome differently. Unintentional walks carry the least value and home runs the most. Pretty simple stuff. However, wOBA also takes intentional walks and sacrifice flies into account when evaluating a hitter. Something other stats do not.

Via FanGraphs, the chart for using wOBA is below:

Above Average.340
Below Average.310

So let’s take a look at the 2016 Pittsburgh Pirates and how things shake out in terms of wOBA. The team leader in wOBA, minus Alen Hanson who only has two plate appearances, is Matt Joyce at .423. Rounding out the top five are Jung Ho Kang (.392), Starling Marte (.373), Gregory Polanco (.369), and David Freese (.352). The bottom five are Erik Kratz (.000), Michael Morse (.000), Cole Figueroa (.156), Jason Rogers (.266), and Chris Stewart (.267).

Hopefully this article as beneficial for anyone who was not previously familiar with wOBA. As I said above, I believe a strong argument can be made that wOBA is the best stat to use when evaluating hitters. As the best stat for evaluating hitters most certainly is not batting average or OPS.

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