Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN
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NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
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Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post
What are Guardian Caps? NFL's latest padded helmets for added safety
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Puffy, spongy Guardian Caps could help curb NFL head injuries - The Washington Post