Nathan Gilbert armed himself after his brother got into an argument in the Royal Oak, in Westwood, on December 22, said Alexis Mercer, prosecuting.
Gilbert, aged 34, came out of the pub holding the tool behind his back before confronting a group of more than ten young men.
When another man tried to disarm him, Gilbert struck him at least four times on the head.
Ms Mercer said his victim suffered 'quite nasty injuries' as the wounds exposed his skull and he was taken to hospital.
Although he didn't want to make a statement, or support the prosecution, CCTV and witnesses identified Gilbert as the culprit.
She said: “The photographs of the injuries speak for themselves,.
She added that the offence has a starting point of 18 months in custody which exceeds the magistrates’ sentencing powers.
Nichola Thorpe, mitigating, said Gilbert, who has no previous convictions, pleaded guilty at the earliest opportunity.
She said: “It is extremely out of character.
“He wasn't involved in the initial incident.”
She said Gilbert urged his brother to go home but a number of people blocked them in the pub car park on Palmerston Street.
Ms Thorpe continued: “He tells me some verbal threats were made.
“He made the ill decision to take the metal bar from the footwell of his car.
"His intention was to disperse the group.
"He can’t explain why he took the tyre iron with him.
"The victim unfortunately stepped forward and there was a scuffle between the two.
"He is extremely remorseful for the way he reacted.
"He has never been before the courts before.”
Ms Thorpe said Gilbert, a father-of-three and who runs his own ground working business, was 'going through a stressful time' following a divorce and has been prescribed medication for anxiety and depression.
Gilbert, of Alfreton Road, Selston, admitted assault causing actual bodily harm and possessing an offensive weapon, when he appeared at Mansfield Magistrates Court, on Tuesday, April 30.
He received a 12-month prison sentence, suspended for one year, with 15 rehabilitation days and a 120-day alcohol monitoring programme.