There are times my personal interest regarding the NFL Combine in matched by belittlement, frequently questioning why a 40-yard dash would be that important for an offensive lineman? We know that they have to do them, but we have yet to understand why people make any big deal with them. With other positions it makes sense, like cornerback, wide receiver and running back -- yet it's still questionable how much stock someone places with the 40-yard dash considering that we're forgetting one trivial and non-important aspect when judging a player's speed. The fact that they're not wearing any pads.
Disregarding my own personal shrug with the annual combine, former Football Outsiders writer Bill Barnwell came up with a metric when discussing the 40-yard dash for running backs. Per FO writer Aaron Schatz (via ESPN In$ider), who explains:
On its own, 40 time correlates with future success less than some fans might expect. But not all 40 times are created equal because not every player is running with the same body. When a 225-pound player runs a 4.48 40-yard dash, it's a lot more impressive than that same 40 time from player who weighs 185 pounds. On top of that, the range of 40 times for running backs is so small (from about 4.2 seconds to 4.9 seconds) that even a minuscule difference can be valuable. Times of 4.41 and 4.51 might look roughly similar, but, in the NFL, holes can close up just that quickly.
Adjust for those factors and you get the formula for Speed Score: (weight * 200)/40 time^4. Multiplying the player's weight by 200 conveniently scales the metric so that an average Speed Score is right around 100. The average first-round pick approaches a Speed Score of 112.
The FO Speed Score correlates towards a degree of success for a prospect, more so than not:
In the past, Speed Score has pointed to the future success of middle-round picks such as Brandon Jacobs (123.5) and undrafted free agents such as LeGarrette Blount (105.8). It has pushed speedy backs such as Chris Johnson (121.9) to the top of their classes and suggested disappointing careers for future busts such as William Green (98.7) and Trung Canidate (99.3). Last year, it suggested that Roy Helu (114.8) and DeMarco Murray (112.6) were middle-round sleepers.
Speed Score is not infallible, of course. The metric struggles with versatile backs who derive a significant amount of their pro value from their abilities as blockers and pass receivers, such as Brian Westbrook (91.7) and Ray Rice (99.7). The exponent means really low scores for backs who are really tiny, under 180 pounds (Dexter McCluster, at 170 pounds, ended up with a Speed Score of 75.0). There's also always a chance a running back simply had a bad day and wasn't at full speed when he ran his combine 40 and thus is better than Speed Score indicates.
This year the speed scores didn't include Trent Richardson because Alabama's former running back choose to run his 40 at his Pro Day on March 27 while recovering from a very a minor procedure on his knee.
That being said University of Miami running back Lamar Miller, generally accepted as the second-best running back prospect and one that the Cincinnati Bengals could realistically select with their 17 or 21 pick, generated the top score this weekend with a Speed Score of 113.1.
University of Cincinnati running back Isaiah Pead scored a 98.7, ranking 11th in the 2012 speed scores.