Lee Nolan (20) left the victim covered in blood and with a fractured nose following the roadside attack.
The victim said his “nose hasn’t been the same” and he has had a problem with smell since the assault.
Judge Deirdre Gearty said the charge was too serious to leave Nolan without a conviction, and she fined him €500.
The judge accepted a conviction could destroy Nolan’s future career and travel prospects, but said he could not go around punching people.
The defendant, of Ballybrack, Kilcock, Co Kildare, admitted seriously assaulting Patrick Lynch at Main Street in Leixlip on February 27, 2020.
Garda Padraig Power told Blanchardstown District Court that gardaí went to the scene shortly before 3am following reports of a brawl.
Gda Power said he spoke to Mr Lynch, who was covered in blood.
Mr Lynch was taken by ambulance to hospital with a suspected broken nose.
Gda Power said Nolan had hit Mr Lynch in the face, leaving him with a fractured nose. A medical report on Mr Lynch’s injuries was handed into court.
Mr Lynch told the court his nose had not been the same since the assault, and he had a problem with smell.
He also has a mark under his eye since the assault.
Defence lawyer Ciaran MacLoughlin said that Mr Lynch told gardaí some girl came up to him. He pushed her away and he got punched.
Mr MacLoughlin said all his client saw was a girl being pushed and he foolishly reacted.
He said Nolan, a dad of one and heavy machine mechanic, was very drunk at the time and did not fully remember the incident.
Mr MacLoughlin asked the judge to consider leaving Nolan without a conviction, saying his client had a good job and a bright future.