Sgt Smellie is due before magistrates in November
A police officer is to be charged with assaulting a protester at the G20 demonstrations in London, the Crown Prosecution Service has said.
Demonstrators posted Youtube footage of a police officer appearing to strike Brighton woman Nicola Fisher.
Ms Fisher, 35, was one of two women to complain about the conduct in April of Sgt Delroy (Tony) Smellie.
Prosecutors say there is insufficient evidence to charge the officer in relation to the second allegation.
In a statement, a CPS spokesman said: "The Crown Prosecution Service has decided that there is sufficient evidence to charge Police Sergeant Delroy (Tony) Smellie with the offence of assault by beating of Nicola Fisher on 2 April 2009 at a demonstration in the City of London."
The CPS reviewed evidence provided by the Independent Police Complaints Commission (IPCC) - the police watchdog - which investigated Ms Fisher's allegation.
The incident happened on the second day of the G20 protests.
Newspaper seller Ian Tomlinson had died during the previous evening's demonstrations.
Ms Fisher was among a large crowd who attended a vigil for Mr Tomlinson.
The mobile phone footage of the protest shows a number of demonstrators close to police officers. Ms Fisher seems to be struck by the back of a police officer's hand.
When she approaches him a second time, he draws a baton and appears to hit her legs with it.
Sgt Smellie was suspended following Ms Fisher's complaint to the police watchdog. He is the first officer to face a charge in relation to the G20 protests.
He will appear at City of Westminster magistrates' court on 16 November.
The Metropolitan Police confirmed an officer had been summonsed to court on suspicion of assault, but would not comment further on the case.
"The officer, who is a sergeant with the Territorial Support Group, is suspended pending the outcome of these proceedings," a Met spokesman said.
He added that officers made split-second decisions to protect themselves, colleagues and the public and were accountable under law and aware their actions were open to scrutiny.
"The decision to use force is made by the individual police officer, and they must account for that," he said.
"It is only right that complaints are thoroughly, and where appropriate independently, investigated so facts can be established. This is vital for the confidence of Londoners as well as our own officers."
A separate investigation is continuing into Mr Tomlinson's death - but prosecutors are not expected to take any decision on the case for some time.