There's a reason why NFL folks sometimes call the NFL Scouting Combine the "Underwear Olympics."
The top performers in each event earn extra attention from NFL scouting staffs and a higher draft slot—and therefore, more money.
The marquee event of the Underwear Olympics, the combine event that moves the needle most, the results everyone wants to see and will quote forever is the 40-yard dash.
What's so fascinating about the 40-yard dash? As many have pointed out over the years, most of these players will never run for 40 yards in a straight line during a game, and certainly not in compression singlets.
What possible difference could a few tenths, or even hundredths, of a second make?
Is there a correlation between 40-yard dash time and eventual NFL success? To find out, I took eleven years of combine performance data (1999-2009) from NFLCombineResults.com.
To make the data set a little more manageable, I restricted the data to the only position group that regularly starts from a two-point stance and sprints straight downfield: wide receivers. The 2009 cutoff is to avoid collecting truncated "career" performance data for the classes of 2010-2012. I also threw out times collected at players' Pro Days; this is combine-only data.
How to measure performance, though?
The best one-number metric of total contribution is Pro Football Reference's Approximate Value. This stat takes into both account a player's production in a season, and for how much of his team's production he was responsible.
The end result is a handy back-of-a-napkin comparison between different players across different years—even across different positions. By adding up current total career AV of all receivers who've come into the league since 1999, we get a good idea of how valuable and productive they've been in the NFL.
Regressing 40-yard dash times against career AV gives us this:
Absolutely no correlation whatsoever.
That "r-squared" figure laid over the scatter plot is what statisticians call the "coefficient of determination." It's used to show how strong of a predictor one factor is for another, or to test a hypothesis, and ranges from one (perfect correlation) to zero (no correlation).
In this case, the r-squared is zero point so-many-zeroes-Excel-needed-letters-to-count-them.
So, no correlation whatsoever.
The player all the way to the right, above 120, is Torry Holt, who ran a 4.44. Nine of the 247 receivers measured ran quicker than Holt and have a career AV of zero. The next highest AV in this group came from Chad Johnson, who ran a 4.57.
One Tool in the Box
NFL teams, to an extent, know there's no direct correlation between pure straight-line speed and NFL production.
So why do they bother measuring it?
Let's go back to the Olympics—the actual Olympic Games last held in London, not the underwear version held in Indiana.
The marquee event of the Olympics is the men's 100-meter dash final. The winner of that race is given the unofficial title of "Fastest Man in the World," and more tune it to watch it than anything else that takes less than ten seconds:
The attraction is obvious: a sprint directly compares person against person in a way no other contest does. The competitors all run to the very utmost of their ability, and the first across the line wins.
Unlike, say, lifting weights or the standing broad jump, sprints are actually exciting to watch. All the while, arms are flying and legs are pumping and robotic cameras are racing to keep up as the fastest people in the world push the boundary of human speed.
What arguably should be the marquee event of the Olympics, though, is the decathlon: a 10-event gauntlet that tests competitors' overall athletic ability: speed, strength, endurance and agility included. Within the decathlon is a 100-meter race, but none of the six heats of decathletes ran a time below ten seconds. Every 100-meter finalist (save Asafa Powell, who pulled up with a thigh injury) ran below ten seconds.
Just as the 100-meter dash helps prove who the best overall athlete in the world is, so the 40-yard dash plays a similar role when determining NFL readiness. A player's suddenness, first three steps and deep speed all play a role in his 40-yard dash time. It's a tool that helps measure overall athleticism, but it's not the only tool.
The key for an evaluator is to know when it's important and when it isn't.
Different Players, Different Concerns
Baltimore Ravens pass rusher Terrell Suggs came out of Arizona State with a reputation as a monster off the edge. Suggs set the NCAA record with 24 sacks, but at his pro day ran the 40-yard dash in somewhere around 4.8 seconds. Suggs' stock may have fallen slightly, but most teams saw his tape and realized deep speed wasn't a problem.
Linebacker prospect Manti Te'o had, without a doubt, the most anticipated 40-yard dash at this year's combine. He'd been an impact defender at Notre Dame, making plays all over the field and nabbing seven interceptions his senior season.
Yet, when evaluators looked at his tape, many did not see great speed. Te'o put himself in position to make plays against Notre Dame's opponents, but his athleticism didn't "pop" off the film the way a player who'll dominate in the NFL often does.
When Te'o ran an official 4.82 40-yard dash at the combine, it confirmed NFL teams' fears. Te'o slow 40-yard time is consistent with the lack of dominant explosion and range teams see on film. That doesn't mean he can't, or won't be a good inside linebacker, but that that's what his ceiling likely is: a good inside linebacker, not a top-10 draft pick.
Winning in March Doesn't Matter
Ultimately, "winning" the Underwear Olympics is much like teams "winning" the draft. A great combine performance might boost a prospect in some scouts' eyes, and he might have a few more coins to rub together after he collects game checks his rookie season.
In the end, though, real NFL money is made by being great on the field. A prospect can put his best foot forward at the combine, but being fast on the track doesn't put you on the fast track.