An attacker was captured after his victim spotted him the next day in Leicester Royal Infirmary.
Both were in the infirmary's accident-and-emergency department for treatment.
Tameer Mitha – who was arrested at hospital – was one of four hooded men who smashed their way into a woman's house in Meadow View, Oadby, on the night of November 6 last year.
They were looking for the woman's ex-partner, who was not there.
The victim, a visiting friend, was attacked after the thugs mistook him for the man they were looking for.
James Thomas, prosecuting, told Leicester Crown Court the householder and the victim spotted hooded men outside the property.
In fear, they hid upstairs in separate bedrooms as the men smashed in the front door. They found the victim.
Mr Thomas said: "The defendant had a metal bar or a bat.
"He grabbed the complainant, demanding to know his name, and struck him on the wrist, knocking a mobile phone out of his hand."
The victim truthfully denied being the man, called Johnny, they were looking for.
The defendant complained of having been given "fake bank notes" by Johnny.
Mr Thomas said: "They went downstairs and the group tried to take the householder's car keys, but the complainant stepped in to stop them.
"The defendant struck him to the side of the face, knocking him to the floor."
The victim suffered a cut to his left ear, swelling to his left cheek and a cut lip, as well as swelling and bruising to his right wrist.
Mr Thomas said: "The next day, while sitting in the accident-and-emergency department, the complainant saw the defendant waiting for treatment to a cut on his finger. He alerted the police."
Officers searched Mitha's home and recovered 31.5 grams of cannabis in a number of individual wraps, with a street value of about £200.
"They were for supply, by him," said Mr Thomas.
Mitha (26), of Hamilton Street, Highfields, Leicester, was jailed for a total of 16 months.
He admitted causing actual bodily harm, having an offensive weapon and possessing cannabis with intent to supply it.
The other three hooded men have never been caught.
In mitigation, the court heard Mitha was easily influenced and had been persuaded by others to take part.
Judge Michael Pert QC said: "You entered someone else's home armed with a weapon and attacked a victim in a bedroom as he, understandably, hid from you and three others who were not even seeking him, but someone else, with a view to attacking them."
He said Mitha played a "leading role" in the attack.
