Bolt is notoriously a slow starter
What?? Bolt would probably run easily close to a 4 flat, nfl combine times are on the runners movement and not on a gun like in track and field.
Actually, he is right, relatively speaking of course. Bolt's "weakness" is the start of the race where he is almost never in the lead until about 30-40 M in, and then he blows the fricking doors open. However, his "slow" start is pretty much a non-issue for an NFL combine because they use a laser timing system, not a gun. Also, there would be other factors that could affect Bolt's time a little bit. Is he allowed to wear his custom spikes, speedsuit, does he run on a track or on turf? Either way, Bolt would be sub 4.2. How far under? No fricking idea.
By the way, Bo's time does not count, since it is a hand time. I would guess that Bo ran roughly 4.38 (since .24 is sometimes added to hand times), but there is no way to know for sure. Chris Johnson's 4.24 is almost assuredly faster.
To the person who mentioned Trindon Holliday, Holliday is not in the same stratosphere as Bolt. Holliday has a PR of 9.95 the last time I checked, while Bolt ran a 9.59. Bolt is a fricking freak. The second fastest person in the world is either Tyson Gay or Asafa Powell, not some football player.