With the one-shell rule gone, here are all the alternate and throwback helmets NFL teams have unveiled so far - Footballscoop
How football helmets fail to protect against some of the most dangerous hits in the game - The Verge
NFL players don Guardian Caps, designed to protect from concussion
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Guardian Caps Guardian Sports
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NFL Should Abolish the 'One-Shell Rule : r/nfl
NFL Should Abolish the 'One-Shell Rule : r/nfl
NFL rescinds one-helmet rule: Here are nine classic throwback uniforms that could return under new policy