Since it doesn't appear that he's ever played the game of football I think the answer is obvious. He'll make more money in endorsements by far as the fastest man in the world. It appears that he may hold this title for a long, long time if he stays healthy. As to the questions about his being legal it seems to me that he isn't fully developed physically as he's only 21 years old. This man has taken speed to a new level and it may be a long time before he's challenged.
So which NFL team will offer Bolt a tryout as a WR? I say Oakland or Dallas. Edit: posted this without reading the last few messages...sorry.
