A policeman was investigating a reported burglary when he allegedly lost his temper and hit Hesan Nejati, now 19, across the head with a torch.
Mr Nejati had tried to break into his own home in Hillingdon, west London, after losing his keys in November 2004.
A jury decided that the policeman, 39, only grabbed Mr Nejati in self-defence and cleared him of racially aggravated assault.
The court heard how the policeman found the teenager in a side alley but allowed him into his home so that he could prove he lived there.
The policeman remains suspended from his job while internal inquiries into their conduct are carried out.
Source: BBC News