Ravens Embrace the Funny-Looking Guardian Helmets - Sports Illustrated Baltimore Ravens News, Analysis and More
Guardian Cap used by football teams to protect against head injury – The Denver Post
NFL Players Experiment With 'Guardian Caps' To Protect Heads
Concussions: Can cap keep football players' heads in game? – Orange County Register
NFL hopes to reduce head injuries with helmet experiment
What Pros Wear: Top 5 Helmets Rated by the NFL & NFLPA - What Pros Wear
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL players experimenting with 'Guardian Caps' to prevent head injuries
NFL hopes to reduce head injuries with helmet experiment