Who is the fastest player in NFL history?

You could certainly make an argument for Bob Hayes. Hayes set the world record in the 100 m at the 1964 Olympics, then joined the Dallas Cowboys as a wide receiver. He was pretty much uncoverable man-to-man. It is widely held that his speed forced opponents to create the first zone defenses. Bob Hayes was the fastest man on the planet in 1964. But Darell Green of the Washington Redskins would have beaten him in a 40 yard dash. Here is my reasoning: Darell Green played 20 years after Bob Hayes. "World Class" speed had improved quite a bit at that point. That was the era (the early 80's) of NFL teams signing Olympis sprinters with no real football experience. When Darell would race those players in NFL skills competitions he would usually win. Also, he caught Tony Dorsett (a 9.9 hundred yard time guy) from behind so easy on a Monday night game that it was actually scary. Just my opinion