Episode 53 of "Stargate-SG1"
s03e09 Rules Of Engagement

Upon exiting the Stargate, SG-1 finds itself in the midst of battle. A group of SG soldiers battle a Jaffa army. Believing the soldiers to be the missing-in-action SG-11 team, O'Neill and the others provide assistance. Much to their surprise, the mystery SG team turns their weapons on SG-1! SG-1 wakes up in the soldier's training camp with headaches and no weapons. The camp's leader, Captain Rogers, assumes them to be from a rival camp until he recognizes Teal'c as Jaffa. Rogers presumes that SG-1 has been sent by the camp's long-gone Jaffa leaders to test their battle readiness. The Captain explains that the soldiers' standing orders are to practice battle using non-lethal Earth weapons until the return of Apophis. O'Neill tells them Apophis is dead. The soldiers don't believe him and resume their war games. As O'Neill and the others try to figure out what to do, the games take a disastrous turn when SG-1's confiscated weapons accidentally make it out onto the battlefield.