(CNN) -- Max Conradt was used to defensive linemen hurtling their 300-pound frames at him week after week. He was a high school quarterback, the team leader who took his licks and got back up.
That is, until the wrenching hit that changed everything.
"It was a vicious hit," said Ralph Conradt, Max's father. "A really bad hit."
Afterward, the 17-year-old got up slowly, staggered for a few seconds, and continued to play. When the game ended, he limped toward the sideline.
"He looked at me and said 'My chin hurts,' " said Joy Conradt, Max's stepmother. "I started to respond and he collapsed. I was absolutely nauseatedly sick with fear."
It was a concussion -- in fact, a handful of concussions over the course of two weeks -- that his doctors believe caused Conradt to sink to the ground, blood pooling dangerously in his brain.
According to the Centers for Disease Control and Prevention, almost 4 million sports and recreation-related concussions occur each year. Experts say the vast majority are suffered at the high school level, but few schools have rules governing how concussion is treated -- and few coaches are trained to identify it.
"It's the group we need to worry about most," said Dr. Jeffrey Kutcher, chairman of the American Academy of Neurology Sports Neurology Section, adding that fewer than half of high schools have access to athletic trainers.
"If there is any suggestion of a concussion, we need to take kids out of the game," said Dr. Stan Herring, team physician for the Seattle Seahawks. "The consequences [of not doing so] can be devastating or even fatal."
The devastating consequences would dawn on Conradt's family members as they sat, breathless, in a closed-off waiting room at the hospital.
"They told us he was going to die," said Ralph Conradt. "He was just a 17-year-old kid playing football. Up until then, I never heard of anyone ever dying in a football game."
In 2008, 16-year-old Ryne Dougherty, a junior linebacker in New Jersey, died after two concussions suffered within a few weeks. The same year, across the country in Washington, 14-year-old David Bosse complained about headache after playing a junior high school game, but returned to play the following week. He died the next morning.
Without a medical expert on the field, coaches and parents are making -- and in some cases not making -- decisions about concussion for which they are ill-equipped, said Herring. That means that post-concussive symptoms like nausea, dizziness, headache, confusion and memory problems are going unchecked.
"We need coaches and parents to understand this phrase: When in doubt, come out," said Herring. "It's better to miss a game than to miss a season ... better to miss a game than to miss the rest of your life."
A study released by the Center for Injury Research and Policy at Nationwide Children's Hospital last year revealed that between 2005 and 2008, about 40 percent of athletes with concussion were allowed to return to play too soon.
The data bore even grimmer testimony about lack of education: During the 2007-2008 season, one in six concussed football players who also lost consciousness returned to play the same day.
"Do you think knowing what I know today that I would have let my son play?" said Ralph Conradt. "Not a chance. Not a chance."
Months after his third brain surgery, Max Conradt was bent over his hospital bed, his back forming the shape of the letter "C." His head lolled precariously -- his eyes trained on what seemed like a far-off place. His lips were moving, but no sound escaped. The tube that helped him breathe hissed and gurgled against his throat.
Conradt survived his brain injuries, but the relief for his family was tinged with grief. Doctors said Max would live, but with the mental capacity of a 9-year-old.
"It's a whole different thing losing your child to a brain injury," said Joy Conradt. "The kid you knew is dead. Somebody completely different is in the body of the child you knew."
Still, experts stress that Conradt's situation is not typical.
"There's a lot of description of possible bad outcomes with concussion and a lot of worry about it. That's appropriate," said Kutcher, director of the NeuroSport Program at the University of Michigan. "The truth of the matter is we have millions and millions of kids who have played contact sports and we haven't seen that link."
Fueled by rage about his son's brain injury, Ralph Conradt lobbied legislators to pass "Max's Law," imposing strong restrictions for returning players to games after they suffer concussion, and requiring rigorous training for coaches.
According to Herring, about two dozen other states also have legislation pending. This week Florida Gov. Charlie Crist announced an initiative designed to reduce sports-related concussions in every U.S. state.
In addition to laws and education, experts say a cultural shift among coaches, players and parents is necessary.
"This whole suck it up and play through it mentality needs to go," said Herring. "Leadership has to come from the coaches, the captains to quit attributing bravery to these injuries. Concussion can be tragic."
It is almost eight years to the day since Max Conradt was released from the hospital. He lives in an assisted living facility and his thoughts often flit back to his "glory days" on the football field. His memories about the concussions that sent his life on its current spiral are scant. But he does know the most chilling details.
"I was sat on by a 280-pound lineman ... he sat on my head," said Conradt, now 25. "When I was walking off of the field, blood was gushing through my brain. I don't remember, but that's what happened."
With the strapping 17-year-old football player he once was a distant memory, today Conradt struggles with basic motor skills, memory and containing occasional fits of rage and depression.
"He gets really, really down when he thinks about what could have been," said Ralph Conradt.
Still, concussion has not dimmed his dreams. Max still craves a challenge. He would like to go back to school. He would like to have some semblance of a normal life.
CNN's Ashley Wennersherron contributed to this report.