"It's part of life; sometimes you're just in the wrong place at the wrong time and that was the end result unfortunately."
Only one punch was thrown, which left Ryan with a black eye.
"There was no melee, there was no fracas or fight or anything like that. When it happened Zac realised that he had hit the wrong person etcetera and that was the end of it.
"Zac got hold of Ryan the next day and he apologised profusely to him and was very sincere in his apology and Ryan accepted that and was happy for it all to stop right there."
Mr Kerr said he decided to speak to media in order to set the record straight about what had happened and to put an end to rumours, such as that it was a fight over a gambling debt.
"There was all sorts of other things flying around ... it was just ridiculous."
Mr Kerr said Ryan wanted to move on from the incident.
"Initially we were pretty upset but I was more upset that it got out to the media later on after Ryan and Zac had spoken, and Ryan wanted just to leave it there."
Mr Kerr hoped Guildford, too, would be able to move on.
"I don't know Zac at all. As a rugby player he's just phenomenal, I've always been a great admirer of his.
"I'm sure - well he is - very remorseful for what has happened. It's a hell of a shame for a young guy his age and like everybody we're just hoping that he can get himself sorted out and get the help he needs and we're certainly hoping we haven't seen the last of Zac in an All Black jersey."
Guildford, who has played 10 tests for the All Blacks, has been involved in a string of high-profile incidents over the past 18 months, including a drunken rampage in Rarotonga in November 2011 that resulted in his arrest. He ran naked and bleeding into a bar before assaulting two patrons.
The Napier-born player then admitted he was struggling with a drinking problem and vowed to give up alcohol for 12 months.
He has gone into hiding since allegations of the latest incident emerged this week and has withdrawn from the Crusaders to seek treatment.
August 2011: Broke team rules when he left the All Blacks' hotel to go out after their Bledisloe Cup victory against Australia at Eden Park. Within weeks, he drank heavily and broke the team curfew after the All Blacks' 25-20 defeat to the Wallabies.
September 2011: Guildford admitted to having issues with alcohol and promised he would get problem under control.
November 2011: The 23-year-old was arrested after he stormed into Trader Jacks in Rarotonga naked and allegedly punched two men. He then announced a self-imposed 12-month drinking ban, saying: "I need to sort myself out.''
November 2012: After being photographed drinking at a function, Guildford said he had changed his ways and now trusted himself to enjoy one or two drinks with friends.
