NFL players experiment with Guardian Caps // Guardian Sports
Why are NFL player pads getting smaller? - Quora
Guardian Caps - Are the soft-shelled football helmet covers effective at limiting head injuries? - ESPN
NFL reports reduction in concussions among players who wore Guardian Caps in preseason - The Athletic
NFL players experiment with 'Guardian Caps' to protect heads - Seattle Sports
Guardian Caps leave some NFL players and coaches with concerns: 'You feel like a bobblehead'
Colin Kaepernick - Wikipedia
Guardian Cap: What are and why the NFL asks this safety measure in helmets
Seeking to reduce head contact, NFL mandates use of Guardian Cap helmet for early portion of training camp - ESPN