This is a symbolic action to indicate that Paul will no longer try to teach the Jews there about Jesus. He is leaving them to God's judgment. (See: [[rc://en/ta/man/translate/translate-symaction]])
Here "blood" stands for the guilt of their actions. Here "heads" refers to the whole person. Paul tells the Jews they are solely responsible for the judgment they will face for their stubbornness if they refuse to repent. Alternate translation: "You alone bear the responsibility for your punishment for sin" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-synecdoche]])
The word "clean" here is a metaphor for Paul being innocent of wrong against either the people or God. Alternate translation: "I am innocent" or "God will not punish me when he punishes you" (See: [[rc://en/ta/man/translate/figs-metaphor]])