Wow!- What an accident.
If one was to apportion blame from a legal point of view, It is clearly the 2nd chaps fault.
Series of lead ups as Accidents dont just happen. ( in no particular order)
1. Clowning around
2. Safety Distance to short
3. Camera etc (what was going on before- speed trials ?)
4. Over familiarity of area
5. Primarily bad observation skills
6. Excessive speed

"Id rather have a bottle infront of me than a frontal labotomy"