wOBA Definition
wOBA stands for Weighted On-Base Average. The credit for the creation of this statistic goes to Tom Tango, an influential figure in the baseball statistics community, and the stat has quickly become one of the most important offensive metrics. Not only is this statistic referenced on its own to demonstrate batter performance, but it is also used in the calculation of other statistics, such as wRC.
The Concept of wOBA
So much of what has happened in the last decade or two in baseball statistics comes down to properly crediting players for what they achieve on the field. While baseball has had plenty of statistics since its inception, many of those stats fail to paint an accurate picture.
Take, for example, the classic statistic we’re all familiar with: batting average. To calculate batting average, you simply divide the number of hits a player has collected by their total number of at-bats. It’s quick and easy, and it immediately demonstrates the frequency a player gets a hit.
Unfortunately, batting average is deeply flawed. All hits are not worth the same value on the field, so weighting them evenly fails to represent the value that each hitter offers. Like batting average, wOBA is a rate stat, but it effectively captures a much clearer picture of offensive contribution.
For instance, in 2017, Dee Gordon hit .308 for the Miami Marlins, while Freddie Freeman hit .307 for the Atlanta Braves. If you only looked at batting average, you’d come to the conclusion that these hitters were roughly equal. In reality, that is not the case. Freddie Freeman hit 28 home runs on the season, while Dee Gordon hit 2. When the specific types of hits are taken into the equation, it immediately becomes clear that Freddie Freeman was the far more valuable hitter.
This is the issue that wOBA sets out to solve. By weighting the outcomes of at-bats appropriately, it’s possible to gain a clearer understanding of which hitters are contributing the most to their teams. In that same 2017 season, Freddie Freeman recorded a wOBA of .407, while Dee Gordon was at .312. We’ll get into how those numbers are calculated in a moment, but the gap between their two performances is now evident thanks to the design of this statistic.
Why is wOBA Important?
If you’re familiar with traditional baseball statistics, you may be thinking that we already have a stat to weight various types of hits – slugging percentage. And to an extent, you would be right. Slugging percentage does value types of hits differently, but it falls short in a couple of ways.
For one thing, the weights are linear, which does not reflect the actual value of each type of hit (a home run is not four times as valuable as a single, but it’s calculated that way for slugging percentage). Also, slugging percentage does not credit a batter for getting on base without recording a hit, such as when drawing a walk or being hit by a pitch. Thanks to the weighting system employed by wOBA, batters are properly credited for what they accomplish.
How is wOBA Calculated?
In order to calculate wOBA, you’ll need to look up the “run value” for each type of outcome. Run value is the value, expressed in runs, that a given at-bat adds or subtracts. A home run adds significant run value, of course, while a strikeout has a negative run value. These values change slightly from year to year based on the run environment but you can find up-to-date numbers at FanGraphs.
Once you’ve located the constants for the year in question, the calculation itself is relatively straightforward.
Here is what the equation looks like for the 2018 season:
wOBA = .69 x uBB + .719 x HBP + .874 x 1B + 1.232 x 2B + 1.554 x 3B + 1.986 x HR / AB + BB – IBB + SF + HBP
- uBB = Unintentional Walk
- HBP = Hit By Pitch
- 1B = Single
- 2B = Double
- 3B = Triple
- HR = Home Run
- AB = At-bat
- BB = Walk
- IBB = Intentional Walk
- SF = Sacrifice Fly
Each type of outcome is multiplied by its run value and those totals are added together. That total is then divided by the total number of at-bats, walks (minus intentional walks), sacrifice flies, and hit by pitches. The result of this calculation will be a rate which represents the player’s wOBA for the season.
What is a Good wOBA?
Generally speaking, a wOBA over .400 is an elite performance, and anything above .350 is generally going to place a batter among roughly the top 50 hitters in the league.
Below are two tables showing the wOBA earned by the very best players of all time as well as in a recent season:
All-Time wOBA Leaders (1900-2018)
| Player | Season | wOBA |
| Babe Ruth | 1920 | .598 |
| Babe Ruth | 1921 | .575 |
| Babe Ruth | 1923 | .571 |
| Ted Williams | 1941 | .568 |
| Babe Ruth | 1926 | .551 |
| Babe Ruth | 1924 | .549 |
| Babe Ruth | 1927 | .545 |
| Barry Bonds | 2002 | .544 |
| Rogers Hornsby | 1925 | .540 |
| Lou Gehrig | 1927 | .540 |
2018 wOBA Leaders
| Player | wOBA |
| Mookie Betts | .449 |
| Mike Trout | .447 |
| J.D. Martinez | .427 |
| Christian Yelich | .422 |
| Alex Bregman | .396 |
| Jose Ramirez | .391 |
| Nolan Arenado | .391 |
| Paul Goldschmidt | .390 |
| Brandon Nimmo | .385 |
| Trevor Story | .384 |
What are the Problems with wOBA?
There are only a couple of minor drawbacks to mention with regard to wOBA.
First, the stat only takes into account what a batter does at the plate, meaning stolen bases are not part of the equation. So, going back to the example from earlier, Dee Gordon would receive an overall offensive boost when taking stolen bases into account, as he is one of the fastest players in baseball. However, wOBA is designed simply to measure performance at the plate, so stolen bases fall outside of that scope.
The other point to mention here is the lack of park effects. If a player enjoys a hitter-friendly home environment, his wOBA will likely be inflated as compared to similar hitters who play in pitcher’s parks. For a park-adjusted look at hitter performance, while still including wOBA, wRC+ is a great choice.