The "mighty" here refers to Saul. The shield was defiled because it fell on the ground, and because the king's blood was shed on it. (See: [[rc://en/ta/man/translate/figs-metonymy]])
# From the blood of those who have been killed, from the bodies of the mighty, the bow of Jonathan did not turn back, and the sword of Saul did not return empty
Saul's sword is spoken of as if it were a living thing that could return on its own. Rather than return empty, it was carrying the blood of Saul's enemies that it killed. (See: [[rc://en/ta/man/translate/figs-personification]] and [[rc://en/ta/man/translate/figs-litotes]])