Sotah, chapter 8, mishnah 6. This mishnah concludes the process that took place before going out to war. It opens by quoting the verse: "V'hayah k'chalos hashotrim l'daber el ha'am" - and when the officers have finished speaking to the people, "ufakdu sarei tzva'os b'rosh ha'am": they appointed commanders of the army, like generals, at the head of the troops.
"Uv'akevo shel am":
The mishnah continues the idea and adds to the wording of the verse, that officers are stationed at the rear of the army as well. The role of these fighters is described in what follows: "Ma'amidin zekifin lifneihem va'acheirim me'achareihem" - they station zekifin in front of the fighters, and others behind them.
What are 'zekifin'?
There are various explanations. The word is certainly connected to the root 'zokef', as in the morning berachos: "zokef kefufim" - who straightens the bent, sets a person upright. According to several commentators these were mighty fighters, men of valor, whose job was to help those who were about to fall and set them back on their feet.
But these men also held another implement: "V'kashilin shel barzel b'yadeihem" - iron axes in their hands. "V'chol hamevakesh lachzor" - and anyone who seeks to flee the battle, "harshus b'yado l'kape'ach es shokav" - the zekifin are permitted to strike his legs with the axe.
"Shetechilas nisah nefilah":
The reason this matters so much, to the point of permitting such a violent act, is explained in the continuation of the mishnah: "Shetechilas nisah nefilah" - for the beginning of flight is a fall. At first glance one might have expected the opposite - that the beginning of the fall is flight; that is, that defeat begins with running away. For once men begin to flee, it becomes contagious: everyone panics, the war is lost, and the fighters are struck down and even killed, Heaven forbid. It is therefore critical to hold the fighters in place.
The mishnah proves the idea that losing the war stems from fleeing from two verses:
"Nas Yisrael lifnei Plishtim v'gam magefah gedolah haysah ba'am" - Israel fled before the Philistines, and as a result there was great slaughter among the people; they were killed by the enemy because they fled.
"Ul'halan hu omer" - and further on it says: "Vayanusu anshei Yisrael mipnei Plishtim vayiplu chalalim" - the men of Israel fled before the Philistines, and they fell slain.
In summary: in this mishnah we learned the final stage of preparation for war: appointing commanders of the army at the head of the people and at their rear, and stationing the 'zekifin' in front of the fighters and behind them - raising up those who are buckling and about to fall, and forcibly preventing flight from the battle. The basis of it all is that "the beginning of flight is a fall," and hence the great importance of making sure that men do not run away from the battle.