Four Mil Mi-28 attack helicopters of Russia's Berkuty ("Golden Eagles") aerobatic display team were performing their routine at the Aviamix air show when one of them crashed. One crew member was killed, but amazingly the other got out with relatively minor injuries (you'll see him stagger out of the wreckage in the latter part of the video). I suggest you watch it in full-screen mode to see all the details.
It looks to me as if the main rotor flexed during the maneuver, impacting the tail rotor and knocking off a couple of its blades. You can see the damaged tail rotor as the helicopter descends.
May God have mercy on the soul of the dead aviator. I hope the Golden Eagles and Mil can find out what happened, so they can prevent any recurrence.