FRIDAY, Aug. 27 (HealthDay News) -- Tommy Mallon was hard-charging through his final high school lacrosse game in San Diego, running full-tilt downfield in pursuit of a ball.

Mallon, then 18, didn't see the opponent who was also digging after the ball. The two teenagers collided hard, and he went down.

To onlookers, it seemed like a normal hit, except that Mallon stayed down longer than usual. His mother, Beth Mallon, was on the other side of the field photographing other players and didn't see the hit. When she zoomed in with her lens and saw that the teen on the ground was her son, and that he wasn't getting up, she experienced a sinking feeling.

"My initial reaction was definitely concern when he didn't get up because he's a tough kid and a tough competitor," she said.

Mallon started to get up but fell back to his knees. The back of his head felt numb. He took off his helmet and threw it aside.

Just then, a certified athletic trainer reached Mallon and forced him to lie back down. "She would not let him up even though he wanted to get up," Beth Mallon said. "He wanted to get up and continue play."

She credits the trainer with saving his life.

Mallon had sustained a major concussion, the third one of his high school sports career -- the first having occurred playing football as a sophomore and the second as a junior, playing basketball. Besides the concussion, which occurred in May 2009, he also fractured one of the vertebrae in his neck and dissected his vertebral artery, one of the arteries that supply the brain with blood.

"In a hit that did not look bad at all, if he had been allowed to get up, he would have been dead or he would have been on a ventilator," his mother said.

Mallon was placed on a spine board and taken to a hospital. "Because of the concussion, he started to vomit immediately when he was loaded into the ambulance," his mother said. "They had to keep rolling him onto his side on his spine board."

After MRI and CT scans, he was taken to the intensive care unit. "He was in a lot of pain -- pain from the neck fracture and headache pain," his mother said. "He was confused. Mostly he continued to vomit. The vomit was overwhelming. They were trying to get the vomiting under control."

In fact, Mallon threw up for most of his first hospital stay, which lasted more than two weeks. His doctors worried that the vomiting would shake loose a blood clot that had formed around his damaged vertebral artery or do further damage to his neck fracture.

Since then, Tommy Mallon has been in and out of the hospital. He spent three months in a cervical collar and another three months in a halo after his neck degenerated further.

But he is alive and well and has started college. He had planned to play lacrosse for Chapman University but instead is attending the University of San Diego so he can remain near his neurosurgical team.

"He can never play contact sports again," his mother said. "He's lucky to be alive and walking."

But Beth Mallon frets about the long-term damage her son might have suffered as a result of all the concussions occurring one after the other. "We won't know neurological damage for a while," she said. "He hasn't had to retain information or organize information until now, where he's in college. Even though the physical aspects have healed, we won't know about the cognitive effects."

"It's pretty scary to think about what's ahead for him after such a serious brain blow for the third time," she said.

Beth Mallon has founded a nonprofit organization, called Advocates for Injured Athletes, to provide a support network for the families of young athletes hurt in play. She also has lobbied for stringent athletic trainer certification in California.

"We want people to know that you can never just assume because a hit doesn't look bad that it's not bad," she said. "He wanted to get up. Everyone who saw the hit thought it was no big deal. And it could have killed him."