NFL hopes to reduce head injuries with helmet experiment - Seattle Sports
Guardian Caps NFL: What player positions are required to wear them?
Why are some Titans players wearing Guardian Caps during training camp?, Titans
NFL Introduces Guardian Caps At First Week Of Training Camp - The Sports Credential
Guardian cap' to prevent head injuries mandated for practices, CFL says
NFL rejects use of PU 'Guardian Caps' in regulation play
A new sight at Baltimore Ravens training camp: Guardian Caps - CBS Baltimore
Guardian Caps NFL: What player positions are required to wear them?
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games