A chef was the victim of an unprovoked attack as he walked in Llandudno town centre late at night - and ended up with a double fracture of the lower jaw.
Judge Rhys Rowlands said that he was simply in the wrong place at the wrong time.
The attacker Daniel Pledge was warned that people had been killed in single punch cases like that and defendants had ended up on manslaughter charges.
As it was, victim Paul Kieron Smith had been seriously hurt.
Pledge, a 31-year-old contractor of Scarisbrick New Road in Southport, denied a charge of wounding following the incident at about midnight on December 20 last year, but he was unanimously convicted by a jury at Mold Crown Court.
Judge Rowlands remanded him in custody to be sentenced next Wednesday.
The judge told the jury that the trouble with such offences was that “when you punch someone in this way you can often end up on a manslaughter charge.
“People drop to the ground unconscious and fracture their skulls. Potentially it is very serious.”
He refused a bail application by defending barrister Michael Whitty and said that it would be an inevitable custodial sentence.
The judge told Pledge: “You have been found guilty on pretty overwhelming evidence.”
He was drunk, out in the street and it was all too common.
“You just picked on a man who happened to be in the wrong place at the wrong time. You thought you were clever. It was a very heavy punch,” he said.
He had caused serious injury but it could have been a lot worse.
Prosecuting barrister Karl Scholz said that the victim was walking along Mostyn Street laughing at something on his phone.
The defendant, a complete stranger, asked what he had been laughing at, the victim replied that he could laugh at anything he liked, and was suddenly punched.
The victim told how the blow knocked him to the ground and it was the combination of the blow and hitting the ground that caused a double fracture of the lower jaw.
He could feel a big gap in his teeth and believed he had lost consciousness temporarily.
But he was able to point out the defendant to police who attended.
He ended up having surgery under general anaesthetic to fix it with plates.
The victim told how he was still in pain, his jaw was numb, and he needed dental work.
Pledge claimed that he had punched out once in self-defence but that punch was ineffectual.
He alleged that the punch which caused the damage was delivered by a second man who left the scene.
Mr Whitty said that another man could be seen on CCTV footage leaving the area at the time and said that his client had remained at the scene.
The victim told how he had been with a cousin to watch the Liverpool v Everton match in a local pub and had four pints.
He was walking alone near a kebab shop when the unprovoked attack occurred.
He said the defendant delivered one blow and that there was no second man.
Pledge and some of his friend who were working in the area had been to the Conservative Club to watch the game that night. He said that he had five or six pints but was not drunk.
After the verdict the court heard that he had previous convictions and when he was 17 he had headbutted and punched a stranger at a taxi rank.
Mr Whitty said that his client was a family man with one child of his own and four step-children.
He asked for bail and said that a prison sentence could be suspended.
But the judge said that an immediate custodial sentence was inevitable and revoked his bail.