That teen was taken to the hospital after the incident. Police say she is being treated for her injuries, but her condition is unknown.
Parents and students are now praising the efforts of a vice principal at the school for helping subdue the suspect.
"We were around the softball bleachers and then we see our vice principal running towards something and then we're like, 'what's going on? Kind of goofy. What's going on?'"
Audrey Kirkhart, a student at Northgate High School in Walnut Creek, describing the moments after officials say a ninth-grade boy stabbed a ninth-grade girl.
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"We knew somebody was bleeding and we were just scared, like what happened? Maybe it was just an injury or something but once we heard somebody got stabbed... we were like, this is crazy what's going on?" said Kirkhart.
Officers say they received a call from the school at 1 p.m. saying that there had been a stabbing. Tamara Biener says her son heard the commotion and then saw a vice principal not only help catch the teen stabbing suspect but hold him down until police arrived, too.
"Our vice principal was the one able to tackle him," said Biener.
"Somebody told me that he ran after the attacker because he tried to runaway and I just talked to him confirming that it was true. He had to hold him down before authorities got there," said Christian Alvarado who is a junior at Northgate.
"My son, he just got out of a class he saw the gentleman, the vice principal choke holding him," said Biener.
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The victim was taken to a nearby hospital. Police now saying they believe the stabbing was an isolated incident involving just the two students.
Parents and students alike say they are proud of the heroic actions of their vice principal.
"It makes me feel better about him personally," said Alvarado who continued, "that just makes it better that he's willing to put his life on the line for the school."
"Our vice principal and principal, they are just amazing - they do great things for this community," said Biener.
The teenage suspect here is facing attempted murder and mayhem charges. He is being held at the Contra Costa Juvenile Hall on no bail.
Anyone with any information is asked to contact Walnut Creek Police Department at 925-943-5844 or call the Anonymous Tip Line at 925-943-5865.