The former Saved By The Bell star stands accused of one felony count of reckless endangerment and misdemeanour charges of disorderly conduct and carrying a concealed weapon for allegedly stabbing a man in a bar in Wisconsin on Christmas Day last year (25Dec14).

Diamond denies the charges, claiming he was defending his fiancee Amanda Schutz, who is facing a misdemeanour disorderly conduct count over the incident.

The actor's trial got off to a false start on Wednesday when his lawyer Thomas Alberti arrived at Ozaukee County Circuit Court with "Good luck to Dustin & Amanda" written on the rear window of his car.

When Judge Paul Malloy learned of the message, he gave Alberti five minutes to remove it from his vehicle, saying, "I'm telling you right now, any more shenanigans like that and you'll find yourself in contempt faster than fast."

Alberti told CBS 58 News, "They're just good people. I want to put on a good defence for them. What they did wasn't wrong. We're going to prove that in court, and no more messages on cars. We'll do it in the courtroom."

The trial continues.