A TEENAGER told police he “saw red” and stabbed a man who he thought was trying to rob him.

The 17-year-old, who can’t be named for legal reasons, is on trial for the murder of 24-year-old Arnold Potter in the Maidenbower area of Crawley.

Witnesses saw the boy boasting with a knife, and prosecutors say he was a cannabis dealer who had two mobile phones.

At his trial at Hove Crown Court, Rowan Jenkins, prosecuting, said the defendant had inflicted a fatal stab wound on Mr Potter during the course of a struggle.

Mr Potter begged the boy to stop by saying “allow it”, and fled.

But then the boy “lost control” by pursuing and stabbing Mr Potter for a second time in the back.

He told officers: “I saw red, I had no control. It was all like instinct.”

The second wound would also have been fatal on its own, and Mr Potter was found dead in Watson Close, sparking a police murder inquiry.

Mr Jenkins said the incident unfolded in the autumn darkness from 6pm onwards on November 15 last year.

He told jurors: “This was a deliberate attack with a lethal weapon, even if he did have concerns about being hurt at the time.

“We do not believe, from the evidence you will hear, that it was necessary for him to take the knife out of his bag and strike out. It was unreasonable in the circumstances and the force used was grossly disproportionate.”

On Monday Judge Jeremy Gold QC had warned jurors not to hold “preconceived ideas” about knife crime after rising public concern.

Mr Jenkins accepted that Mr Potter himself was “involved in drugs” in Crawley and told jurors: “The consequences of that may well not surprise you at all.”

He said that the boy will claim he acted in lawful self defence, and said witnesses had heard Mr Potter discussing the idea of robbing the boy earlier in the night.

The boy believed he had a knife held to his throat, and then was walked along a road with a knife in his back, before breaking free and striking Mr Potter.

But Mr Jenkins says there are no witnesses who saw Mr Potter himself with a knife. He told jurors: “This was fast-moving, confusing and an event with a shocking outcome.”

The boy denies murder, and possessing a knife without a lawful excuse in a public place. The trial continues.