For this installment of Stat of the Week, we’re talking about weighted on base average (wOBA), which is OPS on steroids.
OPS is a simple stat used by a lot of people to measure offensive quality, but it is a messy and inefficient way to do that. OPS is On Base Percentage (OBP) PLUS Slugging Percentage (SLG), but OPS captures the flaws in each of those statistics and does nothing to fix them.
OBP is superior to batting average because it includes walks, but it still treats singles, doubles, triples, and homeruns equally. To OBP, all hits are created equal even though they are not. SLG has the opposite problem in that it weighs hits improperly. A triple is not worth 50% more than a double and a homerun is not worth 4x as much as a single. Those numbers, while simple to understand, do not accurately reflect each type of hit’s outcome on run scoring.
So how does wOBA help? Basically, using linear weights (i.e. math), wOBA properly aligns each hit to a proper value. The formula looks like this and is adjusted each year to reflect changes in the game:
wOBA = [(0.69 x BB) + (0.72 x HBP) + (0.88 x 1B) + (1.26 x 2B) + (1.60 x 3B) + (2.08 x HR)] / PA
Try not to memorize the numbers. Try to understand the ratios because the precise values vary year to year. Here’s a calculator with the 2013 constants for you to play along at home.
What you can see here is that a single is worth about 60% of a double as opposed to half. And a double is more than half a homerun. This might seem counterintuitive at first, but if you think about it, it makes sense. A double will drive in as many runs as a triple, so the only difference is how often the batter would score. Heck a double drives in as many as a homerun except for the batter.
wOBA looks a lot like the other slash line numbers, so here’s a scale to judge. .290 is bad, .320 is average, and .400 is great.
wOBA is a great metric because it tells us what we want OPS to tell us, but it does so in a more accurate way that reflects how things really work over the course of a season. If you’re looking for a number to judge a player’s offensive output, this might just be the one.
A couple downsides, which are evident in other stats, are that wOBA doesn’t include any corrections for era or park. We’ll have to wait for wRC+ to include that stuff.
So next time you want to see how a player is performing, try wOBA and you’ll have a lot more information than batting average and even OPS.