Fellow at work rides with this group; he was at another track when this happened.  You can see the green rider signal and slow up to pit right around 0:13 seconds.  The lead rider slowed unexpectedly and caught the coach off guard.  Six broken ribs and a punctured lung.  The guy filming the video was dazed but unhurt. 

saw this on facebook last week.  that would suck.  a lot.

That was at Pitt Race (formerly BeaveRun) north of Pittsburgh. I know the coach whose bike went airborne. Evidently a red flag had just come out and the rider in front slowed quickly. The coach didn't see the red flag and tried hard to avoid the unexpectedly (to him) slowing guy in front. Amazing that no one got hurt really bad. What an insane video.

Ouch!  They preach and preach at the early morning rider's meeting not to quickly check up when you see a red flag.  Rather, gently roll off throttle and start waiving your left arm as a warning (like the initial rider in the video).

I hope the coach heals up well and gets back out there.

In 2011, I witnessed a guy lose his arm (VIR - slid under the armco) and another guy die (Barber - head first into wall) at a track day.  After 10 years on-and-off,  I hung it up after that and sold the track bike.