The first garda to be tried in connection with the "Reclaim the Streets" protest last year appeared in Dublin District Court today.
Garda Keith Goff, from Mountjoy Garda Station, denied assaulting Mr Brian Hayden at the rally on Dame Street in Dublin on May 6th 2002.
Mr Hayden, a student, said the atmosphere had been jovial for the most part, but scuffles later broke out between gardaí and demonstrators.
He told the court he saw one man being beaten with batons by two or three officers and he had been hit on the head from behind.
Video evidence of the event is to be shown at a later stage in the trial, which is expected to end later this week.
Seven gardaí were charged after the operation to break up the protest in which 24 people were arrested after baton-wielding gardaí moved in.
Fourteen people were injured in the Garda operation, which was recorded by cameramen and photographers. Protesters allege gardaí used excessive force.
The trials of other gardaí charged in connection with the incident are due to begin later this year.