Guardian Caps debut at training camps throughout NFL
Truth About Guardian Caps
NFL players wear Guardian Caps to reduce head trauma during training camp
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
Guardian Caps', NFL's Most Recent Attempt At Preventing Head Injuries
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
Steelers debut new, safer helmets for off-season training
Guardian Cap: What are and why the NFL asks this safety measure in helmets
NFL hopes to reduce head injuries with helmet experiment - Seattle Sports
Arizona Cardinals defensive end J.J. Watt not fan of the new league-mandated Guardian Caps on helmets