NFL executive hints that Guardian Caps could eventually be worn in games, along with position-specific helmets
Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
EXPLAINER: NFL using helmet caps for player safety, research
Guardian Caps NFL: What player positions are required to wear them?
NFL Health and Safety Fact Sheet
NFL players wear Guardian Caps to reduce head trauma during training camp
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Executive Hints Guardian Caps Could Eventually Be Worn In Games - RealGM Wiretap
NFL exec suggests Guardian Caps worn to protect players during practices could one day debut in games
Bear Alexander escaped to USC thanks to one loyal mentor - Los Angeles Times
Number (sports) - Wikipedia
Rising concussion awareness leads one high school to invest in high-tech football helmets, Sports