The Rules of Engagement are the code of battle during a young Jaffa's training, as dictated by Apophis. The Final Challenge is the day in a warrior's training when he is issued a real weapon, first blood is shed, and the games become real.
Shortly after the defeat of his two motherships in Earth's orbit, Apophis brought young soldiers from different worlds to a remote planet to be trained by Jaffa masters. The Jaffa had captured SG-11 on P89-534 and tortured them for information about Earth in order to train the young warriors to duplicate SG units. Under the command of Captain Rogers and Captain Nelson, the young trainees were left with in'tars, a type of training weapon, and standing orders to practice the exercises of battle until the return of Apophis, in preparation to infiltrate the Tauri.
According to Article 7 Section 3, once the battle has commenced, it cannot be stopped, and the troops remained fiercely loyal to their training and their mandate despite SG-1's attempts to end the exercises. However, when SG-1 used a vo'cume to convince the soldiers that Apophis was dead, the war games ended, and the young soldiers were free to return to their homeworlds.
Cross Reference: Apophis, Lieutenant Hibbard, In'tar, Jaffa, Captain Nelson, Kyle Rogers, Vo'cume
Episode Reference: Rules of Engagement