Concussions among players who wore Guardian Caps over summer dropped more than 50%, NFL says - ESPN
Could Guardian Caps be used in games? - NBC Sports
How one Mass. high school is using Guardian Caps
Guardian' helmet caps help protect Herd linemen, Marshall Sports
EXPLAINER: NFL using helmet caps for player safety, research
What are Guardian Caps? Shadow Hills football using new device to reduce head injuries
Guardian Caps debut at NFL training camps around the league
The impact of 'Guardian Caps' on player safety
Football Guardian Cap draws mixed reviews from players, experts for safety effectiveness - The Daily Tar Heel
Guardian Caps NFL: What player positions are required to wear them?
NFL hopes to reduce head injuries with helmet experiment - The San Diego Union-Tribune