A police officer accused of three counts of assault on a man in Gwynedd has gone on trial.
PC James Burns, 55, is also accused with his colleague PC Robin Humphreys of trying to pervert the course of justice by later giving false statements about the incident.
They both deny the charges.
Caernarfon Crown Court court heard the officers were called to an anti-social behaviour incident at Penrhyndeudraeth, Gwynedd, on 10 April 2016.
When PC Humphreys tried to arrest Michael Stanley he ran off, the court was told.
He called for back-up and PC Burns and a colleague responded, with Mr Stanley detained and led to a police car in handcuffs.
Matthew Curtis, prosecuting, said as officers tried to get Mr Stanley into the vehicle, PC Burns grabbed him by the throat.
He said the incident was being recorded by a body camera worn by another officer at the scene, and the footage was shown to the jury.
It showed Mr Stanley sitting in the rear of the car before PC Burns opened the door and sprayed him in the face.
"It was not necessary and entirely disproportionate," Mr Curtis said, claiming the spraying constituted the second assault.
He then walked to the passenger side and again sprayed Mr Stanley, prompting the third alleged assault charge.
The jury was shown the entire body cam footage, including the subsequent journey to the custody suite.
"He couldn't wipe his face and he repeatedly head-butted the interior of the police vehicle as a result of being sprayed," said Mr Curtis.
He said officers had viewed the video footage of the incident in the following days, and alleged PC Burns had amended his statement to include the line "you are the old man who sprayed me.
"I will head butt you".
Mr Curtis also told the court PC Humphreys said in his statement he saw PC Burns grab Mr Stanley by the neck only after the prisoner tried to "head butt" the officer.
Mr Stanley was charged with a public disorder offence, assaulting a police officer and damaging the police car but the case against him was discontinued.
The hearing continues.