Antonio Brown's dispute with the NFL over a helmet, explained
NFL Testing Safer Helmets
This might be a dumb question, but why do they wear these extra
Guardian Caps: NFL requires use of helmet cover at training camps
Guardian Caps - Are the soft-shelled football helmet covers
Complaints begin regarding Guardian Caps, despite one important
Researchers test old-style leather helmets vs. modern ones and
The Coat of Arms Added Protection or False Security: Football
Puffy, spongy Guardian Caps could help curb NFL head injuries
NFL hopes to reduce head injuries with helmet experiment
Guardian Caps: Why some NFL players are wearing them in training
Future of NFL safety: Inside Vicis' high-tech football helmet