NFL players don Guardian Caps, designed to protect from concussion
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
Guardian Caps', NFL's Most Recent Attempt At Preventing Head Injuries
NFL Mandate of Guardian Caps - 2023 Season >> Guardian Sports
Why are NFL players wearing padding on helmets at training camp?
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact
Guardian Caps leave some NFL players and coaches with concerns: 'You feel like a bobblehead'
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets