Judge Thokozile Masipa warned people watching the Oscar Pistorius trial in the courtroom next door to hers that it was not an "entertainment place."
She said that she had heard that the people watching in courtroom GC were "cheering, booing, and doing whatever they like".
Judge Masipa reminded the court that the overflow courtroom was an extension of her courtroom and that they had to abide by the rules she had set.
"It is not an entertainment place or picnic place," she said.
The judge called on the security guards employed to do their jobs and enforce the court rules.
Security had earlier removed a young man after he was caught taking pictures inside the court before proceedings began.
The taking of pictures inside the courtroom before the hearing starts is prohibited. The media are only allowed to take pictures once the court session begins.