Here the word "blood" is a metonym for the murder. See how you translated this phrase in [Numbers 35:19](./19.md). AT: "the one who avenges the murder" or "the relative seeking vengeance" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This means if the community judges that the death was accidental then they must save the accused man from the relative who wants to kill him. If the community judges that the death was not accidental, then the relative must execute the accused man. (See: [[rc://en/ta/man/translate/figs-explicit]])