March 10, 2017
Power and Speed
Bill James popularized sabermetrics. Hell, he coined the term. Several of his measures, like runs created, are still in popular use today, and his work has formed the basis for many sabermetric advances. But James created other measures that combine whimsy with measurement.
One is the power/speed number. It attempts to identify players who excel at both. It’s a simple formula: 2 x (HR x SB) / (SB +HR). That’s not #gorymath; it’s not even #goryalgebra, even if you add that it represents the harmonic mean of home runs and stolen bases.
Now, there are plenty of limitations to defining power solely as home runs. It misses all other extra-base hits, of course. And stolen bases as a measure of speed? OK, but we have much more sophisticated ways to measure baserunning than stolen bases, and besides shouldn’t we be looking at stolen bases minus caught stealing? But James wasn’t looking to create the perfect measure of power and speed. He wanted to create an easy, back-of-the-envelope type of calculation. He succeeded.
You need a lot of both home runs and stolen bases to have a high power/speed number. That’s how harmonic means work. A power/speed number of 30 or so will typically lead a league. Mark Trumbo led the majors in home runs last season, but his power/speed number was only 3.8 because he stole just two bases. Billy Hamilton was 58-for-66 as a basestealer but his power/speed number was just 5.7 because he hit only three homers. By contrast, Tim Anderson had just 10 stolen bases and nine homers, but his power/speed number of 9.5 was much better than Trumbo’s or Hamilton’s. Balance counts.
The power/speed number is still in use. Baseball-Reference tracks it; you can look up career leaders, single-season leaders, and yearly leaders. The top 10 of all time are Barry Bonds, Rickey Henderson, Willie Mays, Alex Rodriguez, Bobby Bonds, Joe Morgan, Andre Dawson, Hank Aaron, Carlos Beltran, and Craig Biggio. The top 10 single-season power/speed numbers belong to Alex Rodriguez, Alfonso Soriano, Eric Davis, Rickey Henderson, Barry Bonds, Jose Canseco, Bobby Bonds, Barry again, Davis again, and Soriano again. The leaders for last season were Mike Trout (29.5), Jonathan Villar (29.1), Mookie Betts (28.3), Wil Myers (28.0), and Paul Goldschmidt (27.4).
But I want to expand the focus from just individual players. You can calculate power/speed numbers for teams, too. Last year, the top power/speed number in the majors was Milwaukee’s 187.3. The lowest was Baltimore’s 35.3. This should not be a surprise. During a year in which everybody hit a bunch of home runs, the Brewers led the majors in stolen bases with 181, 42 more than anybody else. The Orioles had the fewest, a laughable 19, 16 fewer than anybody else.