I heard about this story on The Herd with Colin Cowherd at lunch today.  According to this article:

During a scrimmage Crawford was matched up against LeBron James...and dunks on him. High School prospect Dwight Powell sets the scene:

They were split into teams, and LeBron had his own team. In all the college player’s eyes, I could see a little fire burning, with all of them itching to show what they have against arguably the best player in the world. One player in particular definitely left their mark in Jordan Crawford of Xavier. On an inbounds play, The King was a step slow, and Crawford put a two-hand dunk on him.

I was shocked, but nothing will change my opinion of King James. Jordan Crawford on the other hand has some bounce!"

However the story of the dunk does not end there. After the dunk, LeBron and Nike executives in attendance decided they rather not have video evidence of the dunk get on the internet. Nike officials approached videographers in attendance and confiscated their tapes. This move could have backfired on Nike as the dunk has grown into a legend and has become a hot topic on various basketball related sites on the net.

Jordan Crawford is of course the younger brother of Joe Crawford and was the subject of much conjecture when he transferred from Indiana amidst the Kelvin Sampson debacle.  Its an interesting story.  I havn't dug around enough yet to see if there are videos out there, but from what I'm seeing it looks like the story may be legit.