Multiple police officers were called to the school at 5500 Langdon Street shortly before 10 a.m. Monday.
Chopper 6 flew overhead and showed multiple police cars outside the school.
"I saw what happened. It was really crazy," said Karen Smith, a former student who was visiting teachers at the time.
Smith said she witnessed fights at the school while she was a student, but none that led to a lockdown.
"I just hope it gets better, like, I don't promote violence. I hope Fels gets a change," she said.
There was no immediate word on injuries.