Shaun Raymond Wright (32) pleaded guilty in Mandurah Magistrates Court on Friday to assault in circumstances of aggravation.
The police prosecutor told the court Wright became angry because the victim had a balloon that belonged to Wright�s six-year-old nephew.
An altercation ensued and Wright punched the victim twice in the face.
The victim attended Peel Health Campus with black eyes, a blood nose and a punctured lip where his tooth had gone through.
Duty lawyer Clare Hay appeared for Wright and told the court that he was �disgusted and ashamed� of his behaviour.
She said he had no children of his own but he was close to his niece and nephew.
Ms Hay said Wright had been at the pub for a few hours with his family during a kids� disco.
The victim took the balloon and began taunting Wright�s nephew.
According to Ms Hay, the victim was pretending to bite it and pop it. Wright and his sister approached the victim, Wright felt movement and reacted violently.
Ms Hay applied for a spent conviction as this was Wright�s first criminal offence and he needed a police clearance for his work on the mines.
Magistrate Vivien Edwards said she would grant the spent conviction as she did not want Wright to experience financial hardship if he could not keep his job as a result of the assault.
�Not to say this matter is not serious though,� she said.
She fined him $2000 to be paid to the victim and $169.10 in costs.