Funky-Looking Guardian Caps Rejected by NFL for Regulation Play, OK'd for Practice - Core77
NFL Testing Safer Helmets
Coverage of the NFL in Guardian Caps
Could Guardian Caps be used in games? - NBC Sports
KTTC In-Depth: Guardian Caps in high school football
NFL, players union script a play for safety with Guardian Caps – WHIO TV 7 and WHIO Radio
The Coat of Arms Added Protection or False Security: Football Tests New Guardian Caps to Prevent Concussions
NFL's use of Guardian padded helmet caps in camp draws support and skepticism - The Athletic
Guardian Sports - High Schools Wearing Guardian Caps
Guardian Caps leave some NFL players and coaches with concerns: 'You feel like a bobblehead'
NFL players wear Guardian Caps to reduce head trauma during training camp