Put stock in NFL combine times? Not so fast

It's a straight line. Forty yards. It will take less than five seconds to run.

At the end of that five seconds could be a pot of gold — or a future in doubt. There's no pressure, except your whole life can change the blink of an eye, or only a few blinks of an eye.

But the question for NFL talent scouts is often deciphering which guys are fast when they can run in a straight line without any pads on, and which have a high "game speed" when the lights are on, and tacklers are chasing you from every side.

Former 49ers receiver Jerry Rice is the prototypical example of a player whose 40-yard dash time (reportedly 4.59 seconds) didn't clue teams in to his actual speed in a game.

Thanks to advanced player tracking, the NFL has begun to measure just how fast players are in a game. The data company Sportradar has compiled a list of the fastest players in an NFL game, and looking at just the rookie class of 2017, there was a noticeable divergence between the fastest players at the 2017 NFL combine and the fastest players in games.

Jaguars running back Leonard Fournette had the highest speed of any ball carrier in the NFL, let alone his rookie class, at 22.05 miles per hour. That came on a 90-yard touchdown run against the Steelers in Week 5.

Fournette turned heads at the combine with a 4.51-second 40 time, which was the fastest time by a running back over 240 pounds.

Also standing out was Chiefs running back Kareem Hunt, who logged the 20th-fastest 40 time of any running back at the 2017 combine (4.62). But he recorded a top speed of 20.84 MPH during a 58-yard run against the Patriots in Week 1, good for the fourth highest among rookie running backs and the 13th-fastest running back speed overall on any given play last season.

The players with the fastest 40 times of 2017, T.J. Logan of the Cardinals (4.37) and Joe Williams of the 49ers (4.41) dealt with injuries and did not make an impact.

Vikings running back Dalvin Cook, who ran the eighth-fastest running back 40 at the 2017 combine at 4.49, reached a top speed of 20.45 MPH on a 33-yard run against the Saints in Week 1, the fifth-fastest time last year. When Cook comes back from his ACL injury, one thing to watch is if he is able to repeat the speeds he reached before the injury.

So while fans may fawn over 40 times, and scouts pick apart guys based on a few hundredths of a second, just know that raw speed at the combine might not translate to NFL success, and even a player who appears to run a slow or middle-of-the-pack 40 could be making players chase him when he has the ball in his hands.