Goldenchild you ask what type of bike?
First four words 'my friends 08 Busa.'
Mracer I don't know your friend or you really (met you as the bash seemed pretty smart, for a country feller) so ill assume both y'all have a good head about you. So I just wanna ask.
How often does said friend walk,stoop,look and inspect his bike all of it?
I only ask because in my mind something like this would be a problem slowly building until it finally fell out. Bit by bit ride by ride it got looser and looser until it finally failed. To me I don't see that being fine and tight at start up only to completely come out on one ride. You see what I'm saying?
Looks horrible. Glad he did not get hurt. So many other ways that could have ended, on the back wheel, around a high speed corner, the list goes on. Sorry about the bike too.
Just politely saying maybe only maybe a Pre ride Pre flight check could have caught that?
Wasn't there don't know what happened or how thorough he is. I only suggest because I had something similar happen to me with cheap alum sprocket nuts. Upon Pre flight check I saw two were cracked open and spun off with my hand.
Footnote: I grew up in Tn and consider myself a country feller too so I meant no offense by that.