Simple Sabermetrics: ISO

Crush Davis, atop this season’s ISO leaderboard. Photo courtesy of Keith Allison.

I made it to State Math Field Day competitions. I’m here to tell you that you don’t get past county and regional competition without kicking butt in algebra. [Manly sniff.]

We’re going to do a little algebra in the next 100 words, but I promise to keep it simple.

Fantasy owners need home runs and RBI…power. So what is the cleanest evaluation a hitter’s power?

Consider a player’s triple slash line –  Batting Average .275 /  On Base Percentage .340 / Slugging Percentage .400. Of those three, batting average is the best known, but most generally are familiar with on base percentage as well (OBP). That leaves the player’s slugging percentage as a measure of their power.

But the formula for slugging percentage (SLG) includes singles, and what kind of measure of power uses singles? No power measure of mine, I’ll tell you that!  Juan Pierre and Ben Revere live off the singles. We want a stat that measures doubles! We want a stat that measures triples…uh, actually, a triple is as much a measure of speed as it is power, as it’s kind of a stretched out double. But I digress. We want a stat that measures the dingers!

I give you ISO.

"ISO = (2B + 2*3B + 3*HR) / AB"

If you made it to State Math Field you can handle the Algebra that shows it can also be calculated as follows:

"ISO = SLG – AVG"

Before we go any further I have to confess that I never placed higher than 11th in our state math competition and I grew up in West Virginia, which further cuts out any impressiveness. I guess that’s the difference between MIT and writing for a fantasy baseball blog…

[Pulling himself together.] Let’s continue, shall we! Below is a table to give you a representative ISO sampling:

".000 – .050   Ben Revere, Elvis Andrus, and other guys who rarely hit it out of the infield..051 – .100   Jose Altuve and many under-performers like Eric Hosmer, Justin Morneau, and Miguel Montero..101 – .150   Salvador Perez, Nick Markakis, and Alex Gordon..151 – .200   Joe Mauer and Andrew McCutchen on the lower edge, up to Joey Votto and Ryan Zimmerman..201 – .250   Prince Fielder, Jay Bruce, Yoenis Cespedes, and Mike Trout..251 – .300   Paul Goldschmidt, Carlos Gomez (you better believe it), Domonic Brown and Miguel Cabrera..369             Chris “Crush” Davis"

The game’s beastly power hitters will have an ISO around .300, but anyone with an ISO over .200 is solidly hitting for power. An ISO below .200 indicates that a vast majority of the player’s hits are not going for anything other than singles.

To be clear, ISO does not measure the games best overall hitters, just the guys that hit often for extra bases. But, while not a perfect stat, it is helpful for fantasy owners hungry for homers and RBI (doubles clear the bases).

Little tidbits to help understand it’s uses:

• Avoid players the year following a big ISO spike. The average loss after the breakout was -.060 ISO.
• Using HR/FB in conjunction with ISO helps identify players with real home run potential.
• You often find big ISO increases between the ages of 24 and 29.
• Scan leaderboards for surprises, which could turn into potential trade targets.
• ISO stabilizes at about 160 at bats, meaning a player hitting for power through 160 at bats has a good chance of maintaining the high ISO.

Other Simple Sabermetrics: OBP and SLG, FIP, Command Ratio.