So speculation as ever but given what has been observed so far it seems most likely that:
a) The aircraft was high enough at the apparent point of failure to avoid hitting the TR on any part of the stadium or other fixed object
b) Therefore the failure was likely caused either by something else airborne hitting it - or some sort of separate mechanical failure
Assuming the mechanical failure option, (in the absence of any clear evidence of another airborne object) one thing that still puzzles me is why the pilot chose to lift to such an apparently unnecessary height before attempting to transition into forward flight. Could it be that he was aware of some sort of anomaly on the lift out that made him want to gain extra altitude to have the option of an autorotation away from the confined space of the take-off site? If there was a problem near the ground he would presumably have just put it straight back down - so whatever it was presumably occurred somewhere between the height at which he would normally have transitioned (200ft?) and the height he eventually reached (1000ft?).
To give this theory any validity, there would have to be some sort of anomaly warning (sound/vibration/warning system?) that would encourage the pilot to believe that continuing to gain height enough to attempt a safe autorotation was his best (or only) option. What might this have been?