It was like a 4.6 or something. I saw Giff Smith time him and he ran a 4.6 with an absolutely horrible get-off. That's why 40-times don't often tell the story of how fast a guy really is - if a guy trains specifically for running a 40 with the start and everything (plus it depends on the surface, weather, etc) it will be way different even though his football speed is still the same. Not to mention, Bay Bay might've gotten faster as he developed physically.
Yes. I said this in another post. People assume that speed can't be coached. That is
so not true. You can train to be faster, if it is really necessary. I'd say that anybody who runs a forty under 4.6 is probably already fast enough for most purposes. Mind, if you can train yourself up to go a bit faster, nobody will complain. Still, as Vamos says, there's football speed and track speed. There's a relationship, but it isn't one-to-one. Further, you often don't want the players who are really fast (Cottrell comes to mind) to really turn the burners on until it'll make sense to do so. If Nathan was going full speed from the first step, he'd be outrunning the pitch on every play.
My favorite example of this is Ben Vaughn. Vaughn had been a track star in high school, running the hundred at about 10.6. Then he came to Tech and Buddy Fowlkes saw himself. He took Ben in hand and made him an Olympic athlete running the 100 meters at 10.3 (trucking for those days). He was on the Munich team with Charlie Green and Willie Davenport, two not too slouchy sprinters. Btw, I think Buddy still holds the over-60 record for the 100 at 10.5. Again, trucking.