sheep without a shepherd字面意思一群没有牧羊人看着的羊，引申为群龙无首；乌合之众。

【例句】
The rioters sheep without a shepherd and scattered when the police came.
骚乱者们群龙无首,警察一到便四分五散。

This sheep without a shepherd, just relying on people to bully the weak, nothing tobe afraid of.
这帮乌合之众，只是仗着人多欺负弱小，没什么好怕的。