As Americans grow more aware of the risk of brain injury tied to football — the country’s most popular sport — players and coaches are experimenting with the latest technology in a bid to make the game safer. Advances in training have led to bigger, faster players who have made the high-impact sport more dangerous, particularly at the college and professional level. U.S. football fans have witnessed devastating instances of concussion-related brain damage and even death in players as young as high-school age. They include 16-year-old Ridge Barden, 16, who collapsed after a hit in a game in Phoenix, New York last October and later died at a hospital.