משנה אויף שמואל א 4:17

“And it shall be, when the officers have finished speaking to the people, they shall appoint captains of hosts at the head of the people” (Deuteronomy 20:9). And at the rear of the people they station guards in front of them and others behind them, with iron axes in their hands, and should anyone wish to flee, they have permission to strike his thighs, because the beginning of falling [in battle] is fleeing, as it is said, “Israel fled before the Philistines, and the people also suffered a great slaughter” (I Samuel 4:17) and elsewhere it states, “And the men of Israel fled before the Philistines and fell down slain” (ibid 31:1).