I'm not a rider, but even I know that you shouldn't have another bike on top of you. Like, on top on top.
This incident happened at The Ridge over the weekend. There was debris on Turns 8a and b, which are blind, and the rider who recorded this video slowed down for the yellow flags. Some riders behind him did not.
One rider crashed into another behind the guy recording the video. As you can see, one rider in blue slid past one way, while his bike (on fire) slid another. And then a third dude landed right on top of our rider recording.
Here's the video recorder's description in full.
On my way through Turns 8a and b, I saw flags and marshals standing in the track yelling and waving everyone down at the top of the crest. I assumed there was a rider down in Turn 10 or something, as it's very unusual to have people waving riders down like that. Turned out to be someone's exhaust laying mid-track. I put my hand up, slowed my speed, looked back at the rider immediately behind me while going through Turn 9 and saw that he had also slowed. The larger group of riders further back must not have slowed, because this guy hit me at what felt like full pace when I was doing about 50mph. Speeds through here are generally 110+. The bike that hit me erupted in a ball of flame and at lest 2 or 3 other riders went down behind him. I'm lucky to have rode it out, and hope the riders that went down are ok...
The rider in blue claimed he was fine in a later Facebook post, though his wife stated in the YouTube comments that he got a concussion.
The condition of the other riders is unknown.
(Hat tip to Kevin!)