Prior, fearing that the man had snatched pictures of his own children that he had on his phone, returned to the house.
Defence counsel Jonathan Eaton said Prior allegedly reached through a gate and grabbed the man by his scruff of the neck and demanded to know what photographs he had taken.
Mr Eaton said the alleged assault was so minor that if his client was not a serving police officer, it would never have reached court.
The lawyer said that since it was his client's personal cellphone, also used for Police Association work, it contained personal, private and privileged information, including pictures and details of his children.
The facts were not disputed, he said.
A judge at Christchurch District Court yesterday discharged Prior without conviction.