College programs take proactive approach to helmet safety, All OU Sports
NFL players experiment with 'Guardian Caps' to protect heads
Report: More than 100 diagnosed concussions left out of NFL studies, including injuries to ex-Cowboys QB Troy Aikman
NFL hopes to reduce head injuries with helmet experiment - Wilmington News Journal
NFL players wear Guardian Caps to reduce head trauma during training camp
EXPLAINER: NFL using helmet caps for player safety, research - The San Diego Union-Tribune
Aaron Rodgers explains why he's now at peace with the Packers - Sports Illustrated
Applied Sciences, Free Full-Text
NFL's Decision to Ban Riddell VSR-4 and Schutt Air Advantage Helmets Explained
NFL says positions wearing Guardian Caps saw 52% decrease in concussions - NBC Sports