Ravens Embrace the Funny-Looking Guardian Helmets - Sports
NFL hopes to reduce head injuries with helmet experiment - Seattle
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The story behind those soft-shell puffy Guardian Caps players have
NFL players experiment with 'Guardian Caps' to protect heads – The
What are Guardian Caps and how are they helping football teams?
What are the padded helmets players are wearing at NFL training camps?
NFL hopes to reduce head injuries with helmet experiment
N.F.L. Gives Lower-Body Padding a Tryout - The New York Times
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
Guardian Cap Debuts at Training Camps League-wide
Guardian Caps - Are the soft-shelled football helmet covers
Guardian Caps - Are the soft-shelled football helmet covers