(from this video: ) Any advice on head protection? The best would be easily made from commonly available household items. I haven't found any links with the information, but here are the basics (copied from DMs): The best helmets have an inner/outer shell. Outer protects against sharp things hitting it, inner absorbs shock. "To minimize the G-forces on your soft, gushy brain as it stops, you want to slow your head down over as great a distance as possible. So the perfect helmet would be huge, with 6 inches or mosre of soft, fluffy EPS cradling your precious head like a mint on a pillow." EPS is the inner lining. "The same stuff used in beer coolers, foam coffee cups, and packing material." Outer shells come in two basic flavors: a resin/fiber composite, such as fiberglass, carbon fiber and Kevlar, or a molded thermoplastic such as ABS or polycarbonate, the same basic stuff used in face shields and F-16 canopies."
Boxing headgear, football helmets, whichever, when the head is hit hard enough the brain like a bowl of jelly will move and create all sorts of side effects.