Met Police officer Andrew Ott has been convicted of assault for hitting a student with his riot shield.
Along with two fellow officers, he was cleared of perverting the course of justice.
But PC Ott was found guilty of causing actual bodily harm at Southwark Crown Court.
Protestor William Horner’s tooth was knocked out during 2010 tuition fee protests in London’s Parliament Square.
The policeman was recorded saying ‘I’ve clouted a few’ and ‘I’ll gouge their eyes out’ at the demonstration.
In court, PC Ott said these comments were fuelled by ‘bravado’ and ‘frustration’.
When he was hit by the riot shield, Royal Holloway student Mr Horner was trying to leave a kettled area.
Talking about what happened next in court, PC Ott said : ‘I struck him with the shield, yes [….] He was a threat to me – I dealt with it as I saw fit.’
The student was then arrested for threatening to commit criminal damage, although no further action was taken against him.
Andrew Ott has been on restricted duties during the court case.