NFL enforces helmet ban for Brady, 31 others - ESPN
Can helmet design reduce the risk of concussion in football? in: Journal of Neurosurgery Volume 120 Issue 4 (2014) Journals
Antonio Brown seeks 'Schutt Air Advantage' helmet amid NFL flap: Why it's hard to find
Today's Best Football Helmets: Riddell 360 vs. Schutt Vengeance
What is the door/flap on the top of Green Bay Packers helmets for? - Quora
college football Sports Unlimited Blog
Making Football Safer: Assessing the Current National Football League Policy on the Type of Helmets Allowed on the Playing Field
Talking Helmets With Vicis CEO Dave Marver
Why do some helmets on NFL players have a hexagonal cutout on them (and some do not)? - Quora
10: The Riddell Revolution helmet (left) compared to the early VSR4
What is the meaning of the green dot on football helmets? - Quora
Football Helmet: Most Up-to-Date Encyclopedia, News & Reviews