Baseball by the Numbers—On Base Percentage (OBP) and Weighted On Base Average (wOBA)


This is my second installment of the series on baseball statistics.  This post will cover two stats which measure the value of a hitter getting on base.  On Base Percentage (OBP) measures the frequency of a hitter getting on base in the form of an average.  All of the ways of getting on base, hits, walks, and hit by pitches are measured.  The formula for OBP is H+BB+HBP/AB+ BB + HBP + SF.  A hitter with a high OBP is very valuable; getting on base produces the potential for runs, which are the goal of baseball.  High OBP hitters make good top of the lineup guys hitting in front of the power hitters.  A high OBP guy with speed and base stealing abilities is even better.  OBP gained fame from the movie “Moneyball” in which the OBP was portrayed as a market inefficiency.  OBP was not valued as highly in the early 2000s as it is now, and Billy Beane was able to exploit that inefficiency to his advantage.

St. Louis, MO, USA; St. Louis Cardinals center fielder

Jon Jay

(19) slides into third for a one run triple during the eighth inning of the 2012 NLDS against the Washington Nationals at Busch Stadium. Mandatory Credit: Jeff Curry-USA TODAY Sports

Weighted On Base Percentage (wOBA) takes OBP a step further by placing individual value on each way of getting on base.  wOBA was created by Tom Tango as a way to measure the overall offensive value of a hitter. Unlike Slugging Percentage (SLG) however, wOBA does not use fixed values; the values change from year to year.  The formula is complicated but essentially involves multiplying walks, HBP and each type of hit by a value, adding those totals together, subtracting the negative value of a Caught Stealing (CS) and dividing by the total number of plate appearances.   wOBA is not nearly as well known a stat as OBP.  It is used primarily by those well versed in sabermetrics to compare the offensive values of players.  Because wOBA, like SLG, assigns higher values to extra base hits, power hitters are generally going to have the highest wOBA.

Let’s look at the OBP and wOBA of two Cardinals, Yadier Molina and Jon Jay.  In 2012, Yadier Molina had a OBP of .373 and a wOBA of .375.  These two stats are almost identical. What this tells us about Yadier Molina is that he has the ability to get on base in all the ways possible.  He has power and he takes walks at a good clip.  Molina has always had one of the lowest strikeout rates in baseball.  He makes good solid contact and despite his lack of speed, gets on base a lot.

Jon Jay in 2012 had an OBP of .373 and a wOBA of .341.  As you can see, while Jay has the same OBP as Molina, his wOBA is significantly lower.  What this tells us is that Jay has the same ability to get on base as Molina, but he doesn’t get on base in the same way.  Jay does not have power; Jay hit 4 HR in 2012 to Molina’s 22 HR.  What is interesting about Jay is that he has a lower walk rate than Molina as well.  What is even more interesting is that Jay has the 5th highest HBP rate in all of baseball.  In 2012, Jay was hit by a pitch 15 times.  Talk about taking one for the team to a whole new level.  Whether Jay’s HBP ability is good or bad is a matter of perspective.  If he gets on base, it’s certainly good; if he gets injured in a significant way it’s definitely not good.  Another ability that Jay has is base stealing.  While Jay is not particularly speedy of foot, he does have very good base stealing skills.  Jay stole 19 bases in 2012, the highest of any Cardinal.  Jay was caught only 7 times, which gives him a stolen base percentage of 73%.  Jay gets on base as well or better than any other Cardinal, but he does it in different ways.  His ability to get on base is the primary reason Jay became the Cardinals’ lead off hitter after Rafael Furcal was injured.  So while Jay doesn’t hit like Molina, he gets on base just as much.

I hope you learned as much as I did about OBP and wOBA.  These stats can teach us a lot about the various skills needed to be a good overall major league baseball player and how each player compares to another.  Whatever skill you are evaluating, there is likely a statistic that measures it.  Learning these statistics can add a new dimension to your enjoyment of baseball.