Downhill longboarding is obviously known for it's dangerously high speeds. High speeds give you little time to react to unplanned events unfolding in front of you on the road.
These guys are dhing just like any normal run, but a chicken runs out in the road. Unable to dodge the chicken, one boarder hits it head on, killing the chicken.
This is just another good reason to wear a helmet. Even if you are the most experience skater out there, there are something you can't control...like chickens in the road.