An off-duty police officer was allegedly assaulted last night after attempting to detain a Goonellabah man who had crashed his car while drunk.

"Lismore police will allege that at 11.50pm last night a 39-year-old Goonellabah man was driving along Hillview Drive, Goonellabah, at high speed," a post on the Richmond PD Facebook page said.

"He has crashed his car into a power pole; the impact was large enough to snap the power pole, causing power lines to fall onto the ground.

"An off-duty Casino police officer has seen the 39-year-old leave his car and try to walk away.

The 39-year-old was told to stay where he was and wait for police to attend; he responded by grabbing the off-duty police officer by the throat and tried to push him away.

"The police officer punched the 39-year-old to the face in self-defence then restrained him until police arrived.

"At Lismore police station the 39-year-old recorded a breath analysis almost five times higher than the .05 limit."

The 39-year-old will face Lismore Local Court on charges of Assault and High Range PCA - 2nd + Offence in September.