Guardian Caps - Are the soft-shelled football helmet covers
Helmets don't eliminate concussions. It's time for the NFL to
Ravens Embrace the Funny-Looking Guardian Helmets - Sports
NFL training camps: Guardian Cap players are wearing over helmets, why
Guardian XT Football Helmet Cap, Men's, White/Silver
NFL executive hints that Guardian Caps could eventually be worn in
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What are those caps football players are wearing?
Football Guardian Cap XT – Light Silver/White – Guardian Sports
Guardian Caps: NFL requires use of helmet cover at training camps