C.J. Spiller ran the forty-yard dash in 4.27 seconds at the 2010 NFL combine. This is one of the fastest times ever recorded. Spiller weighed 196 pounds when he achieved this feat. Fast forward to the 2020 combine, in which Jonathan Taylor ran the forty in 4.39 seconds, and one may ask which time is better. Although not as fast as Spiller’s, Taylor’s time might be more impressive. Why? Because he weighed 30 pounds more than Spiller when recording it. Naturally, it’s alluring when a large RB prospect can keep up with his more streamlined counterparts.
In 2008, Football Outsiders created an equation to help us compare the forty times posted by RBs of various sizes in what they called “Speed Score.” The equation is straightforward and calculated by multiplying a back’s weight by 200 and dividing this result by his forty time set to the fourth power.1
While impressive, Spiller’s speed score of 118 falls short of Taylor’s 122. In fact, using a data set that goes back to 2000, only eight RBs have done better. Keith Marshall posted an absurd speed score of 127 in 2016 by running the forty in 4.31 seconds at a weight of 219 pounds. Mario Fannin, a 2011 prospect, posted a time of 4.37 seconds while weighing in at 231 pounds, good for a speed score of 127. Saquon Barkley ties with Knile Davis, Ben Tate, and Brandon Jacobs who recorded scores of 124 and Kevin Jones and Andre Brown managed 123.
As highlighted by these names, a strong speed score doesn’t guarantee success. It does, however, give us a way in which can compare the mixture of size/speed that RB prospects possess. The 2020 class placed just two backs in the 90th percentile; Taylor and A.J. Dillon.