Why 40 yards? 40 yards is the average distance a punt travels. Average hangtime on a punt is 4.5 seconds according to some models. Therefore, if a player runs a sub 4.5 40, he'll be at the spot of the ball before the punt gets there....in theory at least. There are flaws in this methodology. For example, the player must first shed a blocker. Second, 40 times are run without pads, and pads add weight and can slow a player down.
How is the 40 timed? The answer isn't as simple as one might think. For a great, detailed explanation of how it works, click here. Long story short, each player runs 2 40s. For each 40, the time is measured 3 different ways. Scouts often do their own timing and use the official time only as a reference. Hand timing (stopwatch and watching the player) often generated the fastest speeds, due to human error. Now the Combine uses a more automated system, which, while more accurate, is still imperfect in ways. Basically, timers are started by hand and ended electronically once the player hits the end of his run. This system is still error-prone, but is as close to being automated as currently possible.
If you're interested in what average 40 times look like, by position, here's some interesting data that I'll share with you from www.milehighreport.com. Unfortunately, offensive linemen speeds aren't included in this chart, but those aren't overly important from a scouting perspective. For WRs and CBs, average 40 time comes in at 4.48. RBs are slightly slower at 4.49, with Free Safeties at 4.53 and Strong Safeties at 4.55. Outside Linebackers come in at 4.65, and TEs average 4.70. Middle Linebackers tend to be fairly slow at 4.76, DEs clock in at 4.80, QBs at 4.93, and Defensive Tackles are the slowest, at 5.06. No huge surprises here.
What does a fast 40 time mean for a player's long-term NFL prospects? Not much. Since 1999, when electronic timing was introduced for the 40, 16 players have run a sub 4.30 40. Those players are Rondel Melendez, Chris Johnson, Jerome Mathis, Dri Archer, Stanford Routt, Marquise Goodwin, Champ Bailey, Jacoby Ford, DeMarcus Van Dyke, Fabian Washington, Dominique Rodgers-Cromartie, Josh Robinson, Darrent Williams, Tye Hill, Yamon Figurs, and Darrius Heyward-Bey. Out of this list, not many huge names Yes, Chris Johnson has had a great career for a RB, and yes, Champ Bailey could be a future Hall of Famer. However, this list should show that a great 40 does not equate to a great NFL career. The reverse is true as well, a bad 40 time does not equate to a bad career.
What is the 40 actually good for then? Ideally, a player's 40 time can be useful when differentiating between two closely ranked players on a team's draft board. If player A and player B are rated very similarly by a team's scouting department, but player A runs a much faster 40, then the team would likely select player A. It should not be used to replace or significantly alter a team's analysis of a player. A player's true speed is what you see on the field, in pads. Not what you see at the combine in boxers While a player may run a really fast 40, how fast will he run in pads? That's the real question scouts need to consider.
So for all it's hype, a player's time isn't really THAT useful. Yes, teams pay attention to it, and yes, it gets way more attention than it should. At the end of the day, a player's 40 time should be one of the last pieces of the puzzle, and shouldn't make or break a team's analysis of a player. Instead, it should be viewed as one last piece of data when making really tough decisions in the draft room. A player's 40 time shouldn't change the round you select a guy in, but it could be the deciding factor between two very similar prospects. And in the NFL Draft, teams want as much data as they can get.
That's how the 40 works, and I hope this helps clear up any questions about the process! I'll be explaining the other drills as well in future posts, but since the 40 gets so much hype, this one comes first. Let's do some scouting!