NFL introduces Guardian Caps across league to limit number of brain injuries in preseason
NFL: Concussions dropped by more than 50% among players who wore Guardian Caps during summer
Guardian Caps: Why some NFL players are wearing them in training camps
Padded helmet cover shows little protection for football players - Scope
NFL players wear Guardian Caps to reduce head trauma during training camp
Guardian cap' to prevent head injuries mandated for practices, CFL says
Guardian Sports - The Science Behind The Guardian Cap
If a player wanted to wear a Guardian Cap during a game, the league would prohibit it - NBC Sports
Truth About Guardian Caps
NFL hopes to reduce head injuries with 'goofy' helmet experiment
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL players experiment with 'Guardian Caps' to protect heads