The incident occurred Friday afternoon at California State Prison-Sacramento as the guards tried to stop two inmates from attacking another in the yard, said Krissi Khokhobashvili, a spokeswoman for the California Department of Corrections and Rehabilitation. The prison is located in Folsom. The guards initially used less-than-lethal force including 40-millimeter impact rounds, which are similar to rubber bullets in trying to break up the fight, she said.