In another day of simpler statistics, Isolated Power (ISO) is derived from slugging percentage. It’s calculated in the exact same way, but ignores singles. Hence, it is isolating the power of a hitter, defined as the rate at which they get extra-base hits.
Let’s go straight to the formulas.
\text{ISO} = \frac{\text{2B} + 2\times\text{3B}+ 3\times\text{HR}}{\text{at-bats}}
Note that we weight things slightly differently than with slugging percentage, because this also gives us:
\text{ISO} = \text{SLG} - \text{BA}.
With today’s ability to track ball speed and angle off the bat, I don’t think ISO has much place in the game. It is certainly an interesting statistic for getting a sense of how much of a player’s hitting is made up of extra-base hits, but I file it away as “fun to look at, but ultimately inconsequential for comparing players.”
A few pieces of trivia:
The pitcher with the best season ISO, having at least 20 plate appearances, was Lou Sleater in 1957. He had an ISO of .450 due to 3 home runs across 20 at-bats.
Among qualified players1 in the 21st century, Barry Bonds is number 1, 2, and 3 on the list of highest ISO: .536 in 20012, .450 in 2004, and .429 in 2002.
Continue to Day 7 - Batting Average on Balls in Play