If you say that someone is being mobbed by a crowd of people, you mean that the people are trying to talk to them or get near them in an enthusiastic or threatening way. They found themselves being mobbed in the street for autographs
A contraction of the Latin mobile vulgus (the fickle crowd) The term was first applied to the people by the members of the Green-ribbon Club, in the reign of Charles II (Northern Examiner, p 574 )
A highly emotional crowd whose members engage in, or are ready to engage in, violence against a specific target, which may be a person, a category of people, or physical property