(CNN) - Something terrible happened in the third quarter of Pike County High School's football game. But no one knows exactly what.
At first, the team thought Dylan Thomas had suffered a leg injury.
But two days later, the 16-year-old star linebacker died of a head injury.
Now, the rural Georgia county about an hour south of Atlanta is overwhelmed with both confusion and grief.
"We're in a constant process of evaluating the entire thing to see if we can pinpoint one area that maybe this occurred," coach Brad Webber said. "There wasn't anything that really stuck out."
He said officials are reviewing video of Friday's game against Peach County High School to try to figure out what happened.
Ironically, both Dylan and his father were concerned about injuries on the field -- and took extra precautions against them.
'I can't feel my body'
Dylan left the game injured in the third quarter. As he spoke with athletic trainers and the team doctor, Dylan became incoherent and then passed out, Webber said.
First responder Steve Fry said Dylan fell off the bench on the sideline. After the teen went down, he woke up, said "I can't feel my body," and then passed out again, Fry said.
He was taken to WellStar Spalding Regional Hospital and then airlifted to Grady Memorial Hospital in Atlanta. He was pronounced dead Sunday night from a head injury, Superintendent Michael Duncan said.
After Dylan was taken to the hospital, players and coaches from both teams united and knelt to pray for his recovery, Peach County High School posted on Facebook.
The death has sparked an outpouring of support in the county and nearby communities. On Sunday, teammates and community members gathered at Pike Stadium to hold a vigil for Dylan, carrying his No. 32 jersey and bearing the hashtag #DylanStrong.
"He was an incredible young man with work ethic that you can't believe," Webber said. "He was the heart and soul of our defense. Just great student, great family, and the sky was gonna be the limit for him."
'He was always scared to seriously hurt somebody'
Dylan was the "golden child" of his family -- the one who brought everyone together, his uncle Nick Burgess posted on Facebook.
He was the one "that had the biggest heart. The one that told me personally he was always scared to seriously hurt somebody on the field and never thought it would happen to him," Burgess wrote.
Dylan's father shared his son's concern about injuries.
"Dylan's dad took his own money and bought an NFL-quality helmet for Dylan, because he was somewhat concerned about head injuries," Fry said.
The teen's coach said Dylan was wearing a new Riddell SpeedFlex helmet.
Football deaths happen every year
Game-related deaths of football players are rare, but they happen every fall. Last year, of the 4 million young people who played organized football, 13 died from the sport, according to the National Center for Catastrophic Sport Injury Research.
Four of the deaths had "direct" causes from on-field trauma or injuries, and nine deaths were due to "indirect" causes such as heatstroke or cardiac arrest. The 2017 death toll was consistent with football-related fatalities dating back to 2000.
Professional and college football administrators have been increasingly focused on limiting head injuries amid recent concerns that the country's most popular sport is damaging young people's brains.
Efforts to limit concussions and other brain injuries have found mixed results, given the inherent violence of a sport based on large, fast men and boys repeatedly crashing into each other.
But Dylan's death isn't stopping his teammates from playing. Fellow Pike County player Jake Patterson told CNN affiliate WSB that he would honor his fallen teammate on the field.
"I want to get out there and play for him because that's what he'd want for us," Jake said. "He'd want us to play for him instead of just quitting."
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