"As a result of the assault he suffered a cracked head, lacerations to his head, lacerations inside his mouth, two broken teeth and a concussion."
Kirkwood pleaded guilty to injuring with intent to injure with reckless disregard and was sentenced in Whanganui District Court on Thursday.
He was represented by lawyer Raukawa Simon and had the support of his mother in the court.
"She felt that his behaviour was out of character. There is an obvious need for supervision," Simon said.
"It is a serious charge and these were circumstances that were quite concerning obviously for the court and for police."
A pre-sentence report noted that Kirkwood was distraught about what had happened and explained that he was apologetic and remorseful.
The defendant had two previous convictions which the Judge did not consider as serious as this most recent offending.
Judge Sygrove sentenced Kirkwood to five months' community detention and nine months' supervision.
He also ordered Kirkwood to pay $457.14 reparation for medical expenses and $1000 emotional harm reparation to be paid off in four payments of $250.
The Judge said that Kirkwood was lucky that his victim didn't suffer more serious injuries.
"He could have ended up in a more serious state and you would have been charged with manslaughter. You need to keep your fists to yourself in future when you've been drinking.
"The best thing to do when something like that starts happening when you've been drinking with your mates is just run away. Don't get involved in it because it just leads to these sorts of very bad consequences."