‘ And Gaal, the son of Ebed, went out, and stood in the entering of the gate of the city, and Abimelech rose up, and the people who were with him from the ambush.'
When the gates of the city were opened next morning Gaal went out to survey the position, not expecting that his enemy was already near. He had his men at the ready within the city (Judges 9:39). But the opening of the gates was the signal for the attack, so Abimelech and his men rose from their ambush to approach the city quickly before the gates could be closed against them.