Cassondra Singleton's pain is palpable and piercing, as she mourns her son, who was far too young to die.

"It's not supposed to happen," she said, crying outside Cook Children's Hospital Friday. "It's not supposed to happen.

Singleton spent nearly 24 hours at the hospital by her son Aaron's side. The last thing she knew, the 15-year-old, who played JV football for Joshua High School, was off to play an away game in Cleburne Thursday night.

Friends Veronica Zaborowski and Noah Rycroft were at that game. They say they knew something was off after Aaron took a hit.

"He got up, and he walked off the field like normal," Zaborowski says. "He looked a little wobbly, like he'd been hit in the head."

They say trainers eventually came over, and people realized Aaron was having a seizure.

"He was on the bench, and he was sitting really really awkward. And it wasn't right," says Rycroft, who's also on the team.

"My mom said he was seizing for nine minutes," Rycroft says. He says his mother, a nurse, helped at the scene.

"They said he had a blood clot and some swelling. And some of the swelling was in the brain stem," says Robert Gray, who's Aaron's mother's fiance. He considers Aaron a son.

UIL says they don't specifically track football head injuries, but have plans in place to start soon. The family says the only medical condition their son had was asthma.

"Football's such a rough sport. But he wanted to play," Gray says.

Aaron also played baseball, ran track and sang in the choir. His mother says he was working towards becoming an Eagle Scout.

"He will live on through others, because we are going to donate his organs," Cassondra Singleton says. "He would want to be that hero to others."

A person remembered for how much life he had, and how much life he gave, in his 15 years.

Aaron also played baseball, ran track, sang in the choir and played mellophone in the marching band. His mother says he was working towards becoming an Eagle Scout.

At Joshua High School's football stadium Friday night, they honored Aaron. The Varsity team somberly carried his jersey -- number 33 -- onto the field before the game. His teammates wiped away tears, and his fellow band members marked his place in the stands with flowers. Blue ribbons dotted the crowd, sold to raise funds for his family. Even Cleburne fans wore Joshua High School blue in tribute.

"When you're on a football team together, you're like brothers," said Elijah Bols, who brought his jersey to the stadium. "It's a pretty hard loss for the whole team, for the whole Joshua community."