Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN
Guardian Caps, a soft-shell helmet cover, among CFL's new player-safety initiatives
Guardian Cap - Soft-Shell Protective Helmet Cover : Football Helmets : Sports & Outdoors
NFL hopes to reduce head injuries with helmet experiment
Guardian Cap: What are and why the NFL asks this safety measure in helmets
NFL players wear Guardian Caps to reduce head trauma during training camp
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
What's with padded helmet caps teams are wearing
Park High School football blazes safety trail with Guardian Caps
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