Football helmets at Philadelphia-area high schools shed light on growing concussion concerns
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Personalized helmets based on 3D scans could be the future of football
Explaining Antonio Brown's helmet issue: What are the NFL's rules, Raiders' options, AB's contract?
Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
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Football Helmet Misconceptions: Q&A
Riddell's Axiom could be breakthrough helmet for football
New Helmet Technology Aimed to Make Football and Other Sports Safer
Guardian Cap: What are and why the NFL asks this safety measure in helmets
The Football Helmet. Personal Selection, by Brandon Martin