The video shows a man in a light colored shirt during rec time as he walked up to an inmate and started punching another person.
RELATED: Judge rules 3 Santa Clara Co. guards to stand trial for murder in death of inmate
It doesn't take long before other inmates jump in and smaller fights erupt. As many as 20 inmates fight with each other.
"One inmate brushed against another and then the fight was on with fists. You can see a lot of fist fighting going on," said Santa Clara County Sheriff Laurie Smith.
About two dozen deputies rushed to Pod 4A, which is one of the maximum security units. They used pepper spray to break things up.
RELATED: Santa Clara Co. sheriff uses own money to buy cameras for embattled jail
No one was seriously hurt but every second of the fight was caught on cameras, which were installed Wednesday. Otherwise, the jail typically only has one camera per floor.
"It will give us the opportunity to see what actually happened. We'll be able to see who was the aggressor, who was assaulted, who was involved in the fight," Smith said.
Attorney Robert Powell wonders what took so long. He represents former inmate, Ruben Garcia, who claims jail deputies broke his jaw while in custody.
"It will keep the officers honest as well and that's probably the biggest thing, is that they know that they are on camera," Smith said.
RELATED: Santa Clara inmate says he witnesses beating death of inmate
The lock down lasted for hours. Families of those in custody were worried.
"I'm nervous, concerned, extremely concerned for his well-being along with everybody else in there," said the sister of an inmate Kelli Gipson.
Gipson's brother is safe, he isn't on the fourth floor. She hopes cameras will soon be installed on his floor as well.