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AVG/OBP/SLG in an Age of wOBA

Posted By Matt Klaassen On June 27, 2011 @ 3:18 pm In Daily Graphings | 132 Comments

With the increasing popularity of wOBA and other linear-weights-based offensive measures, OPS and its derivatives have become obsolete. That is as it should be. However, three “three slash” (AVG/OBP/SLG) still has its uses. While wOBA and its cousins are to be preferred as an evaluative measure of a player’s offense, the AVG/OBP/SLG combination still has a helpful descriptive role.

For a long time we had a hard time figuring out which of two hitters was better. Sure, we had OPS and OPS+, but we also knew they weren’t quite good enough. For example, two players could have the same OPS but have a different combinations of the beloved “three slash”: AVG/OBP/SLG. In that case, which hitter was better? There was a (correct) sense that OBP was generally more valuable, and measures like The Hardball Times‘ GPA ({[1.8 x OBP] + SLG}/4; invented by Aaron Gleeman) did a good job of getting at that, but it never really caught on for some reason. Of course, linear weights had been around for a while, and Baseball Prospectus‘ EqA (now re-christened as “TAv”) was a rate stat version of those, but for whatever reason neither was widely popular. At least from my perspective, wOBA (Tom Tango’s invention that expresses linear weights as a rate stat scaled to on-base percentage) and its park- and era-adjusted sibling wRC+ have become pretty popular (or maybe I’m just around more “enlightened” fans these days). By giving each event its proper weight and adjusting for the park, we can figure out who performed better or worse per plate appearance.

For example, for years baseball fans were kept awake by this question: which player performed better per plate appearance in 2000: Adam Kennedy (.266/.300/.403) or Rickey Ledee (.235/.322/.381)? Both have a .703 OPS? Help us, sabermetric community! We now know (whew!) that Ledee was better on a rate basis: .310 wOBA versus .304.

Of course, if you’re reading this, you probably understand the general idea behind wOBA (if not, just follow the links above and check out the Sabermetric Library). Today I just want to briefly step back and point out that while wOBA and other linear-weights-based rate stats make the OPS and OPS+ obsolete as more than shorthand for valuing a players’ offensive contribution, taken together, the “components” of OPS, batting average, on-base -percentage, and slugging, (the good ol’ “three slash”) is still helpful as a quick way of describing of what that contribution consists.

I realize that this might be old hat for some, but I think it’s worth having “out there” or newcomers or for people who wonder why someone like me who constantly talks up linear weights still mentions a player’s “three slash” in posts.

Most everyone knows why batting average, on-base percentage, and slugging percentage by themselves are inadequate measures of offense, especially when taken alone. Brief examples: Batting average doesn’t differentiate between hits or include walks and hit by pitches; on-base percentage is better in terms of valuing non-outs, but doesn’t properly differentiate between the value of events (e.g. a walk and a single do not have the same average value); slugging percentage differentiates between hits, but doesn’t take into account stuff like walks, and the weights of the events aren’t right: a home run is not equal in value to four singles (a home run is actually usually worth a about three). OPS was supposed to improve on this, but still implies the wrong weights.

But since we already have our valuation stat (wOBA), are these numbers still worth looking at? Well, unless you having nothing else available or need to calculate something quickly yourself, I don’t see the point in using OPS. (You can actually get an approximation of wOBA out of the three slash with by doing ((OBP x 1.7) + SLG)/3.) But if you don’t have all the peripheral stats, or want to quickly express what kind of offense a player or team has had, the three slash comes in handy. Let’s take a look at the three-slashes of two teammates with a .380 wOBA in 2010:

Ryan Braun: .304/.365/.501
Prince Fielder: .261/.401/.471

[The .380 wOBA does includes steals from Braun, but it's only a few wOBA points' difference, and the example is close enough for our purposes.]

Don’t focus so much on the actual players, but on the lines. We know from wOBA that these players were roughly equivalent offensively on a per-plate-appearance basis. But the “content” is different. What can we learn without looking specifically at rates? Batting average obviously tells us that Braun relied on more hits, was more of a “contact hitter” than Fielder. You can see that Fielder hit for more power: slugging and batting average aren’t good for valuation, but they do represent coherent sets of events (total bases and hits per at-bat). Because they share a denominator (at-bats), you can subtract average from slugging to get “isolated power,” (ISO) which is extra bases per hit. One might be tempted to do the same with OBP and average to get “isolated patience.” That’s actually a mathematical mistake, since average and on-base percentage don’t share the same denominator. However, it does get at something: Fielder’s line shows that he not only got on-base more, but did it less through batting average than Braun and more on walks and hit-by-pitches.

But what practical use is this? Well, again, if you have a full player page or other data source available, you can look up all the rates and stuff, but a three-slash does give a reasonable snapshot summary of the nature of a player’s contribution. Here are two brief examples the thee slash gives value beyond just wOBA for a manager or fan who doesn’t have the knowledge, desire, or available resources to use more detailed method.

The first example is constructing a batting order. Although it is preferable to get more detail than the three slash and wOBA, you’ll be lucky to get a manager to use wOBA, much less a simulation. You know that you generally wants the best hitters in the top half of the lineup, for exampel. But in this case let’s say you’ve got two hitters projected to hit Braun and Fielder’s 2010 lines, where should they go given that they both have .380 wOBAs? A quick look at the three slash tells you that, for example a player better at taking the extra base is better utilized in front of Braun, as he projects to hit more singles (less ISO, higher average) that will better exploit speed, whereas Fielder’s greater number walks mean the runner doesn’t get to run, and this greater power makes the speed redundant.

The second example would determining which pinch hitter to use. If you have two player with equal expected wOBAs in a pinch-hit situation late in a game, which should you use? If your team is down by one, you probably want the player more likely to hit a home run. However, if you’re down by multiple runs, you want a player less likely to make an out. wOBA itself wouldn’t tell you those things.

There are undoubtedly other uses of the three slash. There are also more detailed ways of breaking down a hitter’s contribution: walk rate, home runs on contact, and more. The way to go when comparing the value of one player’s offense to another is wOBA: there’s not point to using OPS unless you have to However, the components of OPS, the AVG/OBP/SLG “three slash” provides a valuable summary description of the type of offense produced, and that still has its uses even when wOBA is available. This isn’t a problem for wOBA or the three slash, they just have different proper uses. That’s why I still use them both.

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