From Longman Dictionary of Contemporary Englishhuman shieldˌhuman ˈshield noun [countable] someone who is taken and kept as a prisoner by a criminal in order to protect the criminal from being killed, injured, or caught
Examples from the Corpus
human shield• Denis says they're using the children as a human shield.• There was even some laughter when one of the thieves picked up a little girl to use as a human shield. 