Eagles Training Camp Practice Notes
Guardian Cap Debuts at Training Camps League-wide
NFL expands rule against misuse of helmet; Guardian Caps required in regular season, postseason
Why Alabama football players are wearing padded helmets in practice
Guardian Caps Guardian Sports
Get A Load Of These Big Dumb Helmet Helmets
Why are NFL players wearing padding on helmets at training camp?
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Guardian Cap debuts during minicamps in effort to reduce avoidable head contact
EXPLAINER: NFL using helmet caps for player safety, research