it was a clumsy overtaking by the 911, just after the driver change. In an attempt to keep up with the leader, he cut back in on the BMW too early which put him in a spin, facing the oncoming BMW which could not avoid him. It mounted the bonnet, then the roof and rolled over the barrier. V nasty looking.
https://sportscar-info.de/2017/10/08...mg=0#gallery-2
https://twitter.com/stiffy_van_door/...31128001323008