Continuing down the path of advanced hitting metrics, let’s cover a metric called Isolated Power, pronounced ISO for short. While most of the hitting metrics we have reviewed so far attempt to capture a hitter’s value in one all-encompassing number, ISO measures something more specific; power.
ISO Explained
Calculating a hitter’s Isolated Power is incredibly simple. It is measured by subtracting a hitter’s average from his slugging percentage.
ISO = Slugging Percentage – Batting Average
ISO tells us how frequently a hitter produces extra-base hits. This is an important trait to measure because we know that extra-base hits lead to scoring more runs. While there are other metrics that do a better job of measuring a hitter’s overall success, Isolated Power helps us compare one particular skill among players and can provide context when considering their in-game power.
For example, if Player A and Player B both have a .450 slugging percentage, but Player A has a .300 batting average, while Player B has a .250 batting average, this means that Player A had an ISO of .150 and Player B had an ISO of .200. A larger percentage of Player B’s hits went for extra-base hits, which in this case is what ISO is helping us learn.
Generally, a .140 to .150 ISO is average, and .170 to .180 is above average, while the best sluggers in the professional ranks have ISOs above .200.
Summary
Make sure you use this metric in the right context. Teams can use stats like ISO to identify a player’s particular strength in their offensive repertoire, such as power in this case. ISO is not designed to be a catch-all offensive metric. Instead, it should be used to measure one of the many skills a hitter may have.
For example, a hitter with a .300 batting average and a .500 slugging is much more valuable than a hitter with a .200 batting average and a .400 slugging, even though both hitters have the same .200 ISO.
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