Most of the people who drop by LL should have some basic understanding of wOBA. You may not know how to calculate it, or you may know how but have no desire to calculate it, or something else, but we talk about it enough around here that you should kind of know how it's built. As our preferred metric for measuring offensive productivity, wOBA uses the empirically-derived run values of major batting events (singles, doubles, triples...) to spit out a hitter's performance in one neat, tidy number.
It's great, and wOBA gets us a good deal beyond OPS and even the wonderfully informative triple slash line. That the online community has taken to wOBA with the speed that it has is no small feat, if you consider how long it usually takes people to change their minds on even trivial things.
But I've had something paying rent in the back of my mind for a few weeks, now, ever since tango re-posted this list of event run values from 2006 (original source: Appelman, Fangraphs). In the calculation, wOBA sets the run value of an out to be zero. All outs. If you sum up all of a hitter's positive contributions, what you're left with are his outs, and for the average hitter, his outs don't contribute anything. Okay, so the outs actually come out to be worth about -0.3 runs, and this is then used as the baseline for all the other run values, but the point is, wOBA uses a constant for this. Every hitter's outs are considered equivalent.
This is a fine assumption, because by and large, they are. It makes very little difference. But what about when you're dealing with a guy like Ichiro? There are a few things we know about Ichiro that could matter, here:
- Ichiro makes a lot of contact
- Ichiro puts the ball on the ground a lot
- Ichiro is fast
- Ichiro very rarely hits into a double play
Ichiro hits a lot of grounders, and he hits a lot of grounders with men on and fewer than two outs. A groundout with nobody on is worth the same as a strikeout. A groundout with men on will either not advance the runners, which is worth the same as a strikeout, or it will advance the runners or replace one of them with Ichiro, which is worth a little more than a strikeout. (Rarely will an Ichiro grounder result in a guy getting thrown out at third or home.) Some groundouts will go for double plays, but as Ichiro has demonstrated over his career, this is unusual; his double play rate is roughly a third the league average.
So, I have to wonder - is wOBA undervaluing Ichiro a little bit? Given 450 outs a season, if Ichiro's average out run value is just 0.013 higher than the league average, then we're talking about an additional five runs. I could very easily be missing something, of course, and all this may not mean anything at all, but it's been on my mind.
Something else worth noting - the Fangraphs version of wOBA, to the best of my knowledge, does not include reaching on errors. Making defenders mess up is not really a skill, but putting them in position to mess up most definitely is, so contact, groundball hitters tend to reach on errors more often than anybody else. The league average rate of reaching on errors is roughly 0.9-1% of all plate appearances, whereas Ichiro's up at 1.3%, a difference that comes out to another 2-3 runs a season if you consider it part of his value. Remember to consider this and also Ichiro's additional baserunning value when you consider his WAR.
Update: as mentioned in the comments, something I forgot - wOBA does slightly overrate Ichiro's singles, as many of them are of the infield variety, and infield singles seldom advance runners two bases. This makes a small difference, but it's a difference.