Certain NFL players must wear Guardian Caps through second preseason game
Guardian Cap Use a Concern for Watt, Saleh Early in Training Camp - Sports Illustrated
NFL Exec: Guardian Caps Could One Day Become Required in Games
NFL training camps: Guardian Cap players are wearing over helmets, why
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
Guardian Cap Debuts at Training Camps League-wide
NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Funky-Looking Guardian Caps Rejected by NFL for Regulation Play, OK'd for Practice - Core77
NFL rejects polyurethane safety caps for football helmets
NFL expands rule against misuse of helmet; Guardian Caps required in regular season, postseason
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
Guardian Caps: What are they and why are NFL players wearing them? - Sactown Sports