PC James Burns was found not guilty of common assault and two counts of assault causing actual bodily harm against Michael Stanley, 28, in Penrhyndeudraeth, on 10 April 2016.
He was also cleared of giving a false statement about what happened.
He had denied all the charges at Caernarfon Crown Court.
The case against another officer, PC Robin Humphreys, who had been accused of perverting the course of justice, was thrown out earlier in the month.
Judge Huw Rees said there was insufficient evidence to prove he had colluded with PC Burns by giving false statements about the incident.

Michael Patterson was handed the order after being convicted of break-ins in the Levenshulme and Longsight areas of the city.
His "consistent method" was to carry out burglaries after entering rear alleyways, magistrates heard.
The 49-year-old, of Field Bank Grove, Gorton admitted three counts of burglary and possession of a Class B drug and was jailed for 16 months.
The ban, known as a criminal behaviour order, will run indefinitely after his release.
It will ban Patterson from entering rear alleyways with the exception of the one behind his own home.
The order also prohibits him from entering an area of Stockport Road, from Stanley Grove in Longsight up to Albert Road in Levenshulme, and the surrounding streets.
Premises targeted in the break-ins included a takeaway, a solicitors' office and a mobile phone shop.
Nigel Murphy, Manchester City Council's executive member for neighbourhood services, said: "Michael Patterson has used the same technique repeatedly to commit a number of offences and this order will prevent him continuing the pattern."

Norris spoke on Tuesday of plans for a show in the NT's temporary theatre that was "very focused on disabled issues".
He added he was also in talks with "senior writers" about a play on the main Olivier stage addressing similar themes.
Norris was speaking at a public debate on diversity in UK theatre at the NT in London.
Act for Change, which organised the event, revealed statistics that showed over the Easter weekend only one actor with a "visible disability" had been noted across all theatre sectors, (the West End, regional and subsidised). That had been at the National Theatre.
Interviewed on the Olivier stage, Norris said he was considering whether to introduce quotas to improve diversity within the organisation.
"There is a big argument about whether there should be quotas. Across this year we will be testing that to see how desirable it is," he said.
"Our policy is quite simply to reflect this city and this country. That means in terms of gender, BAME [black, Asian and minority ethnic] and disabled. That's not a difficult policy."
Norris said that in 2014/15 the National's BAME on-stage figure was an unusually high 33% - driven in part by shows such as Behind the Beautiful Forevers and Here Lies Love. He said his aim was for 20% in any given year.
He admitted that it was "much harder" to achieve the same figures in permanent backstage staff.
Pressed on the issue of quotas, he said: "The last thing I'm saying is no.  What I want is for this community to represent the country accurately and if that's the best way of doing it then, yes - why not?"
The Act for Change debate was chaired by Shami Chakrabarti, head of civil rights group Liberty.
Panellists included actors Adrian Lester and Cush Jumbo, director Phyllida Lloyd, critic Mark Lawson, shadow culture secretary Chris Bryant and Jenny Sealey, coÂ­â€
A police officer has been cleared of assaulting a handcuffed man with pepper spray after arresting him in Gwynedd.
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A prolific burglar has been banned from all of Manchester's back alleyways.
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National Theatre boss Rufus Norris has said he hopes to stage more work that will focus on the issue of disability.