Large Bubble Helmets Are Guardian Caps, NFL's New Safety Measure
What are the padded helmets players are wearing at NFL training camps?
Guardian Caps: Why some NFL players are wearing them in training camps
NFL hopes to reduce head injuries with helmet experiment
Guardian Caps Guardian Sports
NFL players wear Guardian Caps to reduce head trauma during
Guardian Caps', NFL's Most Recent Attempt At Preventing Head Injuries
EXPLAINER: NFL using helmet caps for player safety, research
Guardian Cap Debuts at Training Camps League-wide
NFL: Concussions dropped by more than 50% among players who wore
NFL training camps: Guardian Cap players are wearing over helmets, why