When Manchester United star Eric Cantona leapt into the crowd at Crystal Palace and kicked a fan who was abusing him, the shock waves reverberated far and wide.
When the incident happened, back in 1995, the bracketing of violence and football was hardly new. But what Cantona did was to cross a line, break a taboo of the professional game that said whatever stick the audience handed out, the players never retaliated.
To get the full impact, think of parallels elsewhere. It's as if Kenneth Branagh, in the middle of a Shakespeare soliloquy, were to climb down from the stage and sit on the lap of a theatre-goer. Or, closer to home, a teacher arrives in class, only to find a student standing at the front hell-bent on conducting the lesson himself.
You will appreciate, then, the impact on me and my students of a recent incident while visiting our local magistrates' court.
We were a big group - around 16 of us - packed into the press gallery above a small courtroom. The chair of the magistrates panel noticed us. Her face was severe and seemed to be turned on us as often as the accused. The group, mostly in their late teens and early 20s, were thrilled to be in the court, and at times it showed. But as soon as proceedings started, any noise died away. Apart from anything else, they were all desperately scribbling notes.
As journalism students on an Access to Media course, their brief was to write up news stories about the cases observed. It was a pretty thin list: drink-driving cases and the odd driving while disqualified. After a while, even these dried up and the court was left with nothing else to do.
At this point, the focus of the chief magistrate shifted back to us. "I'd like to address the students in the gallery," she announced. Ouch! And I thought we'd been pretty quiet.
But instead of a ticking off, we received an invitation. "Perhaps you'd like to come down," she said, "and ask us any questions you have about today's proceedings."
So down we all went - through the back of the wardrobe as it were - and stood in front of the bench for a question-and- answer session that the students really got involved in. And instead of reporting the news, now we were actually making it!