EXPLAINER: NFL using helmet caps for player safety, research
Arizona Cardinals' J.J. Watt critical of Guardian Cap: 'Feel like
What Pros Wear: Guardian Caps What are Those Helmet Covers Being
Puffy, spongy Guardian Caps could help curb NFL head injuries
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Guardian cap' to prevent head injuries mandated for practices, CFL
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Guardian Caps: NFL requires use of helmet cover at training camps
Asked and Answered: June 14
Guardian Caps Guardian Sports
Guardian Caps debut at training camps throughout NFL
Asked and Answered: Aug. 8