A classical example would be the trial of Jesus before Pilate. Pilate's wife tells him, "leave that innocent man alone. I suffered a terrible nightmare about him last night" (Matt 26: 19 NLT). Further into the trial when Pilate fails to mollify the rancid Jewish stampede he capitulates and remarks, "I am innocent of this man's blood. The responsibility is yours" (Matt 26: 24 NLT). The Jewish Sanhedrin, priests and people roar, "His blood be on us and our children" (Mat 26: 25 KJV). It is a blood-curse: a self-invitation of judgment. And the pogroms in history testify how many times it happened, from nation to nation.
A blood-curse happens when in self-righteousness, unjustified anger, vicious vengeance and warped morality we hedge an innocent person. We hound him. We leave him desolate (Jer 20: 1-2), when he was God-sent to heal and transform. It happens, when you reiterate your wrong as right and rabidly silence the innocent person.
A blood-curse is dangerous because it travels through generations. Never engage in a blood-curse.
There is, however, one possible way to overcome a blood-curse. One possible way to overcome the unnecessary bloodshed of the innocent. Read through 2 Samuel 21.