<P> In track and field races, the runner must react to the starting gun, which takes approximately 0.24 seconds, based on FAT timing . A runner with a reaction time less than . 100 is subject to disqualification as that is deemed too fast of a reaction time . For electronically timed 40 - yard dashes, the runner is allowed to start when he wishes, and a timer hand - starts the clock . This aspect means that comparisons with track times are impossible given that a reaction time is not factored in . Furthermore, the use of hand - timing in the 40 - yard dash can considerably alter a runner's time; the methods are not comparable to the rigorous electronic timing used in track and field . </P> <P> Jacoby Ford, who ran a 4.28 s in the 2010 NFL Combine, had a collegiate best of 6.51 s in the 60 - meter dash (outside the top - 40 of the all - time lists). This highlights the difficulties in comparing track running times to football 40 - yard times due to the different timing methods . </P> <P> Auburn's Bo Jackson claims to have run a 40 - yard dash with a time of 4.12 s . A time of 4.18 run by Jackson within the same week added some support to the legitimacy of the times . Texas Tech's Jakeem Grant was hand - timed by a New Orleans Saints scout as running a 4.10 in 2016, potentially beating Jackson's record . Deion Sanders ran a 4.27 - second 40 - yard dash in 1989 . </P> <P> In 2013, Carlin Isles recorded a time of 4.22 at a Detroit Lions facility during a workout . </P>

Who has the fastest 40 yard dash in the nfl ever