This is complete

Darrell Green NEVER ran a sub 4.2 40-yard dash. No one in history has ever done so. Oh, and Green NEVER held the world record in the 100 nor did he ever have the fastest time in the world. Heck, he didn't even win a collegiate title that I could find.
Coles never ran a 4.16 nor a 4.29, yet another myth.
First we have to take into account the errors of hand-timing, both at the beginning and the end of a race. Second, when the time actually starts, with the players motion or with a gun/light. The times you are people are talking about are absurd. I would be happy to go over the normal conversion rate used when hand-timing is involved with anyone interested. Back to the matter at hand:
Ben Johnson, a one-time 60-meter world record holder and one of the greatest starters in history, is believed to have run 40 yards faster than any human in history. Johnson, completely filled with copious amounts of steroids, won the 100 meters at the 1988 Olympics in Seoul in 9.79 seconds, only to have his gold medal and world record stripped after failing a post-race drug test.
Timing officials have since broken down that famed race into 10-meter increments, and Johnson was so preposterously fast that he went through 50 meters in 5.52 seconds and 60 meters in 6.37 – both under the current world records at those distances. He went through 40 yards that day in 4.38 seconds.
He was running in spikes . . . on a warm afternoon perfectly suited for sprinting . . .
with a slight tailwind . . . with years of training from arguably track's top coach, Charlie Francis . . . with Carl Lewis and six others of the fastest men on the planet chasing him . . . with 69,000 people roaring at Seoul's Olympic Stadium . . . with the ultimate prize in sports, an Olympic gold medal, at stake.
And, as we learned later, with muscles built with the assistance of the anabolic steroid stanazolol.
Four-point-three-eight seconds.
Even taken from the moment he moved instead of the gun, Johnson covered the 40 in 4.26 seconds. (A time equaled by Maurice Green in his then record run). I'm sorry, but neither Green nor Coles is a full stride faster than Johnson was.
As for actual NFL times, Sanders was timed at 4.29 in high tops at the combine, but it was hand-timed. It should be noted that all there admit he pulled up at the end, which means he was flat out flying!
OJ SImpson was a member of a WORLD reocrd 4x100 meter realy team and thought to be the fastest on that team. His best electronic, non-flying start 40? A 4.5.
Renaldo Nehemiah to this day, almost 30-years later, holds high school and collegiate records in the hurdles so there is no doubt that he was blazing fast. (Just in case the Olympics and world records weren't enough to convince you

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Those three, Willie Gault, Bob Hayes, and Green were all amazingly fast. None was under a 4.2 though.