Isolating the St. Louis Cardinals' Power-Hitting

For years, if I wanted to know how much power a batter or team hit for, I looked at slugging percentage. The stat recognizes a truth that baseball fans understand on a gut level: all hits are not created equal. Whereas a single and an extra-base hit each have the same effect on a player's batting average, the extra-base hit undeniably puts the batting team in a better position to score runs. In the case of a homer, it guarantees at least one run for the batting team.

SLG recognizes the difference between hit types. The formula for SLG gives singles no weight, but multiplies doubles by two, triples by three, and home runs by four. Here is the formula:

SLG = ((1B) + (2 x 2B) + (3 x 3B) + (4 x HR)) / AB

It wasn't until rather recently that I began to wonder about the accuracy of the SLG stat. Why are we even considering singles if we want to know how much power a player hits for? In short, SLG seems ill-formulated for truly measuring a player's power-hitting.

This was about the point in time when I discovered the Isolated Power (ISO) stat on Fangraphs. The name had immediate appeal to me. Finally, someone had isolated a player's power-hitting. The Fangraphs Glossary entry for ISO explains how succinctly and clearly:

Isolated Power (ISO) is a measure of a hitter's raw power. Or, to look at it another way, it measures how good a player is at hitting for extra bases. The simplest way to calculate ISO is to subtract a player's Batting Average from their Slugging Percentage, which leaves us with a measure of just a player's extra bases per at bat.

By subtracting BA from SLG, singles are removed from the equation. The following formula, which can also be used to calculate ISO, clearly illustrates the difference between how SLG and ISO are arrived at:

ISO = ((2B) + (2 x 3B) + (3 x HR)) / AB

Last year, the Cardinals boasted a potent offensive attack. St. Louis plated the second most runs in the National League. Not surprisingly for such a prolific scorer, the Redbirds ranked fourth or better in each of the traditional "slash" stats of batting average (BA), on-base percentage (OBP), and SLG. The Cards placed second in the National League with a .271 BA, first with a .338 OBP, and fourth with a .421 SLG was good enough for fourth.

2012 NATIONAL LEAGUE TEAM SLG RANKINGS

Fourth in the NL in slugging is nothing to sneeze at. It places the Cardinals in the top quarter of their league in the stat. However, looking at a breakdown of their hits and extra-base hits undermines the notion that the Cards hit for a lot of power last year.

2012 ST. LOUIS CARDINALS HITS BREAKDOWN

The Cardinals ranked fourth in the NL in SLG despite finishing sixth in doubles, sixth in triples, seventh in homers, and sixth in extra-base hits. Clearly, having the third-highest singles total in the NL helped to inflate the Cardinals' SLG. Eliminating singles from the equation using ISO gives a much more accurate reflection of the amount of power the 2012 Cardinals hit for.

2012 NATIONAL LEAGUE TEAM ISO RANKINGS

In 2012, the Cardinals had a very good offense. However, the St. Louis hitters did not hit for that much power. While they placed fourth in the NL in SLG, it was a ranking inflated by the large numbers of singles they hit. In truth, despite having five players with 20 or more homers, the Redbirds only managed to hit for power at a level slightly above average.