Charles Ellicott Commentary Genesis 9:5

"And surely your blood, [the blood] of your lives, will I require; At the hand of every beast will I require it. And at the hand of man, even at the hand of every man`s brother, will I require the life of man." — Genesis 9:5 (ASV)

Your blood of your lives… — This verse should be translated: “And surely your blood, which is for your souls, will I require (that is, avenge); from every beast will I require it, and from man: even from a man’s brother will I require the soul of man,” as from Cain. “Your blood, which is for your souls,” means that it is the means for the maintenance of the animal life within them. Since it is, then, the support of human life, an animal that sheds it becomes guilty and must be slain; and even more so, those animals that prey on humans must be destroyed.

Thus, a command is given for the eradication of carnivores at the time when the more peaceful animals had just been saved. The last clause literally is… at the hand of man, at the hand of one that is his brother, will I require the soul of man. This has nothing to do with the avenger of blood. The close relative is here the murderer, and the commandment requires that even such a one should not be spared.