It seemed like a routine tackle. But No. 18 Josh Nava was slow to get up.
The Riverside Polytechnic High School senior appeared to shake it off and then wobbled to the sideline. But the concussion was so severe the 17-year-old collapsed and flopped under a bench.
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"He came off the field, everything seemed normal, and then he went through concussion symptoms, said Ron Ford, the teen's stepfather.
Nava was rushed to the hospital for emergency surgery to stop the bleeding, swelling, and pressure on his brain.
The 17-year-old had what was supposed to be an added safety measure against concussions -- Riddell's insight impact helmet rimmed with sensors that alerts coaches on the sidelines to hits that could cause brain injuries.
"That censor is in there to kind of monitor the severity of certain impacts and also the frequency of certain impacts as well," said Justin Grayson with the Riverside Unified School District.
In Nava's case, the school district says his helmet's sensor did not go off.
Riddell told ABC News that, "We are hopeful he has a full recovery. Since few facts are known, it would be inappropriate for us to speculate on the circumstances surrounding the incident."
Nava has been in a medically induced coma since his surgery to reduce swelling. But on Wednesday, Nava's brother posted the high school's booster club website that the young player is now breathing on his own.