The leader the English Defence League (EDL) verbally abused a member of the group before head-butting him, a court has heard.
Stephen Lennon, 28, goaded followers during a rally in Blackburn on 2 April, magistrates heard. His victim, Alan McKee, 33, was accused of putting messages online about informers and "grasses". EDL founder Lennon, of Luton, denies common assault, at Preston magistrates' court.
The bench heard Mr Lennon launched a tirade against Mr McKee, calling him a "degenerate mug", before trouble broke out. He was pulled from the crowd for his safety. But he later confronted Mr Lennon about his speech, the court was told. Mr Lennon is accused of stepping forward and head-butting him.
Don Green, prosecuting, showed the court the speech given by Lennon on a DVD, recorded by police. Mr Green said the two men then squared up to each other. After an altercation, "the defendant lunged forward and head-butted Mr McKee once in the face, causing a cut across the bridge of his nose," Mr Green said.
Mr McKee, who was drunk, was arrested and taken away. The court heard he did not want to make a formal complaint and would not be giving evidence in court.
The trial continues.