Mobbing

Mobbing is a special type of consensus bullying behavior. It is about an imbalance of social, physical or other power involving a group or a person.
Mobbing is like a "virus" or a "cancer" that spreads via gossip, rumour and innuendo. Mobbing is developed or pushed by a leader who persuades others into a systematic pattern of "mob-like" behaviour toward the target.
History.
Some European languages have adopted "mob" as a loanword to describe special kinds of bullying. 
Checklists.
A checklist for identify mobbing behaviour includes