SB 6.11.4
kim va uccaritair matur
dhavadbhih prsthato hataih
na hi bhita-vadhah slaghyo
na svargyah sura-maninam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O demigods, these demoniac soldiers have taken birth uselessly. Indeed, they have come from the bodies of their mothers exactly like stool. What is the benefit of killing such enemies from behind while they are running in fear? One who considers himself a hero should not kill an enemy who is afraid of losing his life. Such killing is never glorious, nor can it promote one to the heavenly planets.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Vrtrasura rebuked both the demigods and the demoniac soldiers because the demons were running in fear of their lives and the demigods were killing them from behind. The actions of both were abominable. When a fight takes place, the opposing parties must be prepared to fight like heroes. A hero never runs from the field of battle. He always fights face to face, determined to gain victory or lay down his life in the fight. That is heroic. Killing an enemy from behind is also inglorious. When an enemy turns his back and runs in fear of his life, he should not be killed. This is the etiquette of military science.
Vrtrasura insulted the demoniac soldiers by comparing them to the stool of their mothers. Both stool and a cowardly son come from the abdomen of the mother, and Vrtrasura said that there is no difference between them. A similar comparison was given by Tulasi dasa, who commented that a son and urine both come from the same channel. In other words, semen and urine both come from the genitals, but semen produces a child whereas urine produces nothing. Therefore if a child is neither a hero nor a devotee, he is not a son but urine. Similarly, Canakya Pandita also says:
ko ’rthah putrena jatena
yo na vidvan na dharmikah
kanena caksusa kim va
caksuh pidaiva kevalam
“What is the use of a son who is neither glorious nor devoted to the Lord? Such a son is like a blind eye, which simply gives pain but cannot help one see.”