Quote History I haven't watched it, but does it say that a half-helmet is useless? Because they kind of are. When people crash, they look up and forward to see where they're flying, and they land on their chin/lower face, taking the initial, hardest impact on that part of their skull, with no help from the half-helmet sitting up on top of their noggin. If they landed face-down or chin-down, the helmet would help some, but most people don't land that way.
Multiple dudes I know IRL have been knocked clean out in half-helmets, without even taking much damage to the helmet. One of them was riding alone, and has no memory other than he became aware that he was walking down the trail bleeding. Another was in a group ride, but in back, people realized he wasn't in the group, went back, and there he was not even knowing where he was or who he was. Both times, the initial impact was to their lower skull, the helmet was too high to do much (or anything). I also know multiple dudes that weren't knocked out, but got some definite facial scarring from the initial impact being to their lower face, not the helmet.