Tyler Lewellen, 16, was an incoming junior at Arlington High School.
School officials say the team was involved in a three-way scrimmage with Rubidoux and Fontana high schools last Thursday. At the end of one of the plays, for some reason, Lewellen walked off the field at Rubidoux High School and collapsed.
Lewellen lost consciousness. He was rushed to the hospital where he underwent brain surgery over the weekend. He unexpectedly died at the hospital Tuesday night.
It's unclear if playing football was the cause of Lewellen's death. An autopsy will be conducted to determine how the teenager died.
The entire campus is in mourning.
"Tyler was a wonderful young man with a bright future ahead of him and everything to look forward to," stated Arlington Principal Antonio Garcia. "We are so saddened that he was suddenly taken from us. Arlington appreciates our community's support as we grieve the loss of one of our own."
The Riverside Unified School District brought grief counselors to the campus on Wednesday to help students and faculty cope with the loss.
"He's just one of those guys where it's like you look at him, and you just have to smile. He's always in a good mood," said friend Robert Alvarado.
Alvarado says he has been friends with Lewellen for almost two years. He says he was on the phone with Lewellen's father Tuesday night when the decision was made to take him off life support.
"All you hear were gasps. People were crying immediately. It sucked," said Alvarado.
Alvarado also took part in the scrimmage last week, but he was on a different field when it happened.
"Once we went onto the main field, we saw an ambulance there and everyone was huddled up," he said. "I looked over and I saw that it was Tyler."
Alvarado tells Eyewitness News that other football players have told him that Lewellen was on defense and went in to make a tackle when there was helmet to helmet contact. The school district would not confirm that.
Relying on their faith and each other for support, Lewellen's friends gathered to pray Wednesday night.
Friends say Lewellen demonstrated his strength on and off the field by having the courage to do what's right.
"He was a nice kid. The first time I met him was when I was getting bullied. He was the one that stopped it," said Arturo Camargo.
As the Arlington Lions begin a new season, the players are trying to cope with taking the field without the teammate who made them laugh and had their back.
"His parents were such a great inspiration. The dad said, 'Coach, one thing I'll tell you is Tyler died doing exactly what he wanted to do. When I left him that day, he had a huge smile on his face, and he probably has a huge smile on his face now,'" said football Coach Patrick McCarthy.