Mr Lawson said Judge Mackenzie used factors in the victim impact statement to discount the mitigating factors.
Mr Lawson said factors not properly assessed were the context leading up to the incident, that his client had been "goaded" before the offence, his youth, that restorative justice was offered, his offer to make amends, the plea of guilty and evidence of his good character.
His conviction may jeopardise his ability to travel the United States for future work or education purposes, Mr Lawson said.
"What you have is a young man with real promise, he is a talented sportsman and clearly well regarded in the entertainment industry. He is not just someone who is going to make it but is actually on the road.
"There is no definite plan at this time of future travel to the USA but what is identified is the appreciable situation where that could occur."
Crown prosecutor Andrew Hill said he did not accept the victim provoked the attack as the summary of facts stated Mr Eccleston was struck once on the side of the face and a second time to the back of his head.
"These were the actions of a man not provoking anything but the actions of a man to walk away and take the high road," Mr Hill said.
"The end sentence was conviction and reparation of $500, clearly the mitigating factors were taken on board. The overall assessment of the gravity by Her Honour was correct."
Mr Hill said Judge Mackenzie was right to discount Barker's future need to travel as it was more "possible and maybe" rather than real and appreciable.
Justice Wylie reserved his decision and, if there are no delays, it will be released in about 10 days.
