Making Sense of On-Base Percentage, Slugging Percentage and OPS

Jim Leyland held a microphone on stage in front of a couple hundred fans in Comerica park in January, 2011, professing his philosophy regarding on base percentage:

"On base, on base, everybody talks about on base percentage. Jim Leyland, I like the guys that knock em in. I know, there’s a lot to be said for that. They talk about 'Moneyball' and working the pitcher and on-base percentage. Yes, there’s a lot to be said for that. But my theory is, during the course of a major league game, normally for both teams, there’s enough guys on base. The guys to me, that make the money are the guys that can score them from first and knock em in. I like the slugging percentage, over the on base percentage, myself. That’s just an opinion."

Leyland’s comments reveal a simplistic, if not outdated philosophy to many baseball fans who keep up with advanced statistics. To some fans, Leyland may as well have come out and said the world was flat. Leyland showed a total lack of understanding of the research that has been done on how to measure the productivity of hitters.

My intention here is not to criticize Leyland, nor is it to promote sabermetrics as a healthy lifestyle for all baseball fans. I’d just like to share the location of a very comfortable place that I’ve found in the world of statistics, that has a pretty good overall viewpoint and doesn’t make me dizzy when folks start speaking in saber. I’d also like to make this a place that even a casual baseball fan, one that is intimidated by "advanced metrics" can get to rather easily, without getting queazy. It’s really not a steep climb.

In Part 1, we'll take a look at the method to the madness of on base percentage (OBP) and slugging percentage (SLG) and see if we can give them their due respect on the scale of importance. In part 2, we'll explore why wOBA is a better stat to use than OPS and produce a scale so we can easily see what wOBA is above or below average and how the Tigers' players fit in.

Batting Average (AVG): In the beginning. If you google the term "batting champion," you will come up with the hitter in each league that has the highest batting average, and has at least 502 plate appearances for the season. That player will be declared the "batting champion" in each league. Miguel Cabrera is the batting champion in the American League, but that doesn’t necessarily make him the league’s most productive hitter. Batting average measures the percentage of time that a hitter gets a base hit. Walks don’t count, and home runs count the same as an infield single. By the way, Cabrera also led the league in on base, on base, on base.

Runs Batted In: "The guys that knock em in," as Leyland calls them, do make the big bucks in the baseball market. But RBI are, to a great extent, a function of opportunities. You can’t drive in runs, other than solo home runs, unless there are runners on base to drive in. A typical lineup should be arranged so that the big RBI guys follow guys who frequently get "on base, on base, on base." Leyland happened to be talking about Jhonny Peralta, his 80 RBI, and his value to the team when he launched into his philosophical discussion of on-base percentage. What he didn’t mention was that Peralta led the league in at bats with runners in scoring position the previous two seasons. It should be understood that players who get hits tend to also get hits with runners on base, or in scoring position, at about the same rate, averaged over time.

Slugging percentage (SLG), the preferred statistic of Jim Leyland, is simply the number of total bases, again not counting walks, divided by the number of at bats. Four bases for a homer, three for a triple, two for a double, and one for a single. Slugging percentage has been around at least since I was a kid, and there was a regular column for SLG in the stat charts listed in the Detroit News every Sunday. The problems with SLG are that a triple isn’t really three times as valuable as a single, and a base on balls is treated like it never even happened. If you want to "just knock em in," that’s fine, but a triple doesn’t put three guys on base to knock in. They have to get on base or you can’t knock em in.

Leyland’s reference to "moneyball" when the topic of on base percentage came up (and he actually brought it up) might give us a sense of how one that is resistant to the "new way of thinking" looks at sabermetrics. To some, moneyball and sabermetrics are one in the same. Leyland did make reference to "the guys that make the money" when referring to sluggers. No doubt this is true. Players with big home run and RBI totals get paid more as free agents than players with only a high on base percentage or guys that play solid defense. The movie "Moneyball" features Oakland A’s GM Billy Beane, who tries to field a winner by assembling players that cost less money but have high on base percentages, run the bases well, and play solid defense. So it’s easy to see where Leyland, and no doubt many others, get the idea that "moneyball" and sabermetrics are all about "on base, on base, on base."Actually, that is a gross over simplification of what sabermetrics is all about.

On base percentage (OBP) or on base average (OBA) is an important component in a sabermetrics styled view of offensive productivity, but it is by no means the ultimate statistic to measure a hitter’s value. Unlike AVG and SLG, OBP does take walks into account, but it gives the same weight to a home run as it does to a single or a walk. Obviously, those are events in a baseball game that don’t have the same value in terms of producing runs. Billy Beane was quoted once as saying that OBA is three times as important as SLG. Well, is it? Not from a sabermetrics view point. Sabermetrics isn’t based on money at all. Bill James and the folks that blazed the trail for the development of sabermetrics certainly know that a home run has more value than a walk. It just so happens that players that had an ability to get on base were not paid as well as some of those who racked up RBIs. Obviously, the players who do it all get paid the most.

On base plus Slugging (OPS): Somewhere, half way between traditional statistics and sabermetrics is what Fox sportscaster Joe Buck called "that new OPS statistic." Yes, he actually said that, during the 2011 World Series broadcast. (Notice that I resist the strong temptation to go off on a rant tangent, here, in an effort to stay on topic.) On base plus slugging, or OPS, is just that. Take a player’s on base percentage and add his slugging percentage, and voila, you get OPS. Now, I think that OPS is a very useful statistic ... for sluggers. But it’s still very much a slugger’s stat. OPS gives one base for walks, two for a single, three for a double, four for a triple, and five for a home run. We’re used to seeing OPS being discussed in conversations now when discussing the MVP awards for each league and it's commonly used in baseball discussions these days.

Of course, OPS is not new to those that have been paying any attention at all to the ever evolving world of baseball statistics. In fact, you can go on websites such as Fangraphs and Baseball-Reference and you’ll see OPS+, which adjusts OPS to the league average and adjusts for the ballparks where the players compile their numbers. I suppose we should be thankful that the mainstream media has gotten that far, but we’re just not prepared to leave it at that.

It seems logical that OPS can be improved upon by giving the proper weight to each of the ways that a player reaches base during a season, or a career. What is the proper weight to give each walk, each home run, each single, etc?

Well, if you go to Fangraphs.com, go to the player stats page and you click on "Advanced" (which is code for sabermetrics), you’ll see that there are several statistical categories after each player, but they are sorted according to wOBA, by default. So, perhaps wOBA is to sabermetrics what batting average once was to statisticians of the 1950s and 60s. Probably the most important measure of a player’s offensive value.

We'll explore it further in Part 2.