As Keith Law, in his interesting book “Smart Baseball” points out, we fans want a number to measure and compare the quality of our baseball players’ offense. The trouble is, so many of the numbers we use regularly don’t give us the whole picture.
Batting average (AVG), though traditional and ubiquitous, is perhaps the most flawed of all. On-base percentage (OBP) is more useful, as is slugging percentage (SLG), though the attempt to give us a holistic look by combining those two into one measure, OPS (literally “on-base percentage plus slugging”), doesn’t really work for a number of reasons.
We rely on slash lines of AVG, OBP, SLG, despite their one dimensionality, just as we take our temperature to see if we’re running a fever, knowing full well that the absence of fever doesn’t necessarily mean we’re healthy.
A Better Way To Measure Performance
Law is a proponent of wOBA, short for weighted on-base average, a sabermetric based on linear weights that was created by Tom Tango. wOBA covers all the typical batter’s events (hits, extra base hits, walks, times hit by a pitch, and outs) and it weighs each of those components.
wOBA weights aren’t applied as simplistically as they are with SLG, which wrongly assumes that triples are worth three times more than singles, for example. Instead, weighting for wOBA is systematically determined based on the run scoring environment and updated every year. When certain kinds of are more scarce, the weighting adjustments make these individual feats more valuable and, naturally, the converse is true. When certain events, say home runs, are more plentiful, the weighting reduces their value in the wOBA calculation.
Weighting values using in determining wOBA can be different depending on who is doing the calculating. RSNStats relies upon the weights determined by the Fangraphs web site, which makes them available for all years going back to 1871.
In 2018, the formula for wOBA is (0.690×Unintentional BB + 0.721×HBP + 0.881×singles + 1.250×doubles + 1.582×triples + 2.037×HR) / (AB + BB – Intentional BB + SF + HBP).
What’s a good wOBA?
The formula for wOBA scales it to league average for on-base percentage. This is handy because if you already know what a good OBP is, you also know a good wOBA. In mid-season 2018, the major league average for on-base percentage is .318, so as you approach .400 you’re getting into excellent performance for both measures.
There’s little reason to create a new glossary for stats here at RSNStats.com. Rather, if you’re interested to know more, look into fun Law’s book or check out the explanations available on the Fangraphs, Hardball Times, and Major League Baseball web sites.