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The 40-yard dash is a sprint covering . It is primarily run to evaluate the speed of American football players by scouts, particularly for the NFL Draft but also for collegiate recruiting. A player's recorded time can have a heavy impact on his prospects in college or professional football. This was traditionally only true for the "skill" positions such as running back, wide receiver, and defensive back, although now a fast 40-yard dash time is considered important for almost every position. The 40-yard dash is not an official race in track and field athletics and is not an IAAF-recognized event. 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 from the line of scrimmage, 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. For purposes of measurement at the Combine, the run is made along the lower sideline from the 40 yard-line to the end zone, which has built-in rundown space. In track and field races, the runner must react to the starting gun, which takes approximately 0.24 seconds, based on FAT timing. 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. 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).〔(60 Metres - men - senior - indoor ). IAAF. Retrieved on 2013-05-29.〕 Justin Gatlin was significantly slower at the NFL Combine, achieving a 40-yard dash best of 4.42 s, but holds the fifth fastest 60-meter dash ever with 6.45 seconds.〔Lee, Jimson. ("Justin Gatlin 4.42 40 Yard Dash" ). SpeedEndurance.com, 4 April 2008. Accessed 30 April 2009.〕〔(Justin Gatlin ). IAAF. Retrieved on 2013-05-29.〕 This highlights the difficulties in comparing track running times to football 40-yard times due to the different timing methods.〔(60 Metres - men - senior - indoor ). IAAF. Retrieved on 2013-05-29.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「40-yard dash」の詳細全文を読む スポンサード リンク
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