Several posts saying bad things to the OP, obvious derail on the thread and off topic posts.
This thread has run its course a long time ago.
Physically Intervene, even if it puts me in danger, and attempt to stop the attack.
Call the police to see what happens, even if it may be futile.
Run away from the vicinity of the attack as fast as possible.
Try to talk the attackers out of the attack.
Nothing and just observe.