. . . The origin of timing football players for 40 yards comes from the average distance of a punt and the time it takes to reach that distance. Punts average around 40 yards in distance, and the hangtime (time of flight) averages approximately 4.5 seconds. Therefore, if a coach knows that a player runs 40 yards in 4.5 seconds, he will be able to leave the line of scrimmage when a punt is kicked, and reach at the point where the ball comes down just as it arrives.
Timing method and track comparisons
In terms of judging a person's speed, the best method of timing is through lasers which start and stop the times when passed through. A laser start (from a stationary position) is more accurate for measuring pure speed as it does not register a runner's reaction time. However, the method of timing a 40-yard dash can affect the accuracy by as much 0.5 seconds (with the manual stopwatch method). The National Football League (NFL) did not begin using partial electronic timing (started by hand, stopped electronically) at the NFL Scouting Combine until 1990. . . .