Some additional info: the formation was supposed to ride at 40km/h (25m/h), but some of the guys, apparently under the influence, would accelerate to 100km/h (60m/h) on that stretch of the road. One of them lost control during the stunt and hit another motorcycle. The two bikes crashed and a few more piled up on top of them. The damaged bikes spilled oil, making it even more difficult for others to stop/maneuver. As a result, 15 bikes went down. 12 guys had injuries, 7 ended up in a hostpital, four are in serious condition and one is in critical conditon...
PeteSC gets kudos for correctly identifying the cause of the pile-up as a stunt.