When it comes to evaluating offensive performance, RSNStats focuses heavily on slash lines, a common set of statistics that includes Batting Average, On-Base Percentage, and Slugging Percentage. But there are many more ways to evaluate players. This article describes one of those ways, Isolated Power.
Isolated Power (or ISO), is a simple but telling stat to help you better understand a player’s ability hit for power. The higher a player’s Isolated Power, the more likely they are to belt extra base hits (that is, doubles, triples, and home runs). Players with an ISO of .250 or higher are the game’s premier hitters. Statisticians remind us that ISO requires a large sample size in order to be considered accurate or predictive. Generally, ISO is best measured with 500 or more plate appearances or 1,000 or more at-bats.
To calculate ISO you add up a player’s extra base hits, giving more credit for home runs than triples and more credit for triples than doubles then divide that by the player’s number of at-bats: ((2B) + (2×3B) + (3×HR) / AB). A shortcut that works the same way is to subtract the player’s batting average from his slugging percentage.
The formula for Isolated Power is similar to that of Slugging Percentage, but it eliminates singles from the equation as they do not represent powerful at-bats. Players with very different performances on the field can have identical Slugging Percentages, but it’s their Isolated Power that spotlights the players who are specifically adept at hitting for power.
A player that only hit singles would have a zero ISO. One who only hit home runs would have a 3.000 ISO.
In 2017, average ISO across baseball was .171, with the Astros at an MLB-best .196 and the Giants at a last place .132. The top player ISO for 2017 (minimum 500 plate appearances) was the Marlins’ Giancarlo Stanton (.350). Aaron Judge of the Yankees (.343) owned the top ISO in the American League. Only three other players in baseball had ISOs of .300 or higher in 2017: Joey Gallo (.327), Mike Trout (.323), and Cody Bellinger (.315).
As a team the Red Sox ISO was a weak .149 in 2017, the lowest such ISO in the American League and third-lowest in baseball. Mitch Moreland led the club that season with a .197 ISO, followed by Mookie Betts (.194) and Hanley Ramírez (.188).
The Red Sox all-time best career ISO was .290 by Ted Williams (1939-60), followed by Jimmie Foxx (.285, 1936-42). They’re followed on the club list by David Ortiz (.278, 2003-16), Manny Ramírez (.276, 2001-08), and Jose Canseco (.273, 1995-96). Rounding out the Red Sox Top 10 ISOs of all time are Jason Bay (.260, 2008-09), Babe Ruth (.260, 1914-19), Carl Everett (.238, 2000-01), Mo Vaughn (.238, 1991-98) and Dick Stuart (.236, 1963-64).
At the start of 2018 and with a minimum 1,000 plate appearances, Giancarlo Stanton (.284) owns the top ISO among active players followed by Mike Trout (.264), Khris Davis (.261), Albert Pujols (.256), Trevor Story (.248), Nolan Arenado (.246), Nelson Cruz (.243), Kris Bryant (.241), Miguel Sano (.241) and Chris Davis (.240).