NFL players experiment with 'Guardian Caps' to protect heads
NFL introduces Guardian Caps across league to limit number of brain injuries in preseason
New Rule at N.F.L.'s Camps: No Tackling. It's Just Practice. - The New York Times
NFL hopes to reduce head injuries with 'goofy' helmet experiment
NFL hopes to reduce head injuries with helmet experiment
NFL hopes to reduce head injuries with helmet experiment
NFL rejects polyurethane safety caps for football helmets
Why NFL Stars Are Showing Up to NFL Training Camps—and Not Practicing - WSJ
Hockenson hopes to build on last season's success
NFL players wear Guardian Caps to reduce head trauma during training camp
A brief history of Football helmet technology