The incident happened at Scarva Walk in Banbridge at about 16:00 BST on Friday.
The victim, who is aged in his 40s, was taken to hospital for treatment for head and facial injuries.
Two men in their 20s were arrested and are being questioned by police on suspicion of causing grievous bodily harm with intent.
One of the men is also suspected of assaulting police and causing criminal damage.
He was taken to hospital for treatment for a hand injury.
Det Sgt Colin Patterson of the Police Service of Northern Ireland said: "Anyone who saw this assault taking place and has information that could be useful to police should contact us."

The northbound accident was at 02:30 BST between junctions 11 and 12, near the Oxfordshire and Warwickshire border.
Motorists were held on the road overnight. It reopened at 14:30 BST.
West Midlands Ambulance Service said: "Sadly nothing could be done to save the driver of one lorry, a man, and he was confirmed dead on scene."
The statement added: "A second lorry driver, a man in his 50s, was found to have sustained minor arm injuries and neck pain.
"He was given treatment by ambulance staff before being discharged on scene.
"A third patient, with minor injuries, was treated by our South Central colleagues."

The Pilgrims, second in League Two, will return to England on Thursday.
"We're going there to train for three days in preparation for the remaining games of the season," Argyle manager Derek Adams told BBC Radio Devon.
"I've done it before as a manager. It's about getting us focused with 18 games to go, and allowing us to train in hot weather and a very good area."
Adams added to his squad during the January transfer window, and believes the trip will help integrate his new players.
Jakub Sokolik, Nathan Blissett, Antoni Sarcevic, Ryan Taylor and Matthew Kennedy were brought in as Argyle look to strengthen their promotion challenge.
"It's been in the planning for a while and we've been able to factor it in," said Adams.
"We've got new players in and it's about trying to get them to know what the other players are about, and also to get my ideas across to them."
Sarcevic, signed from Shrewsbury during the final days of the window, added: "It's nice to get away from everything and get a good few days in Spain. But it will be hard work."

Stephen Jamieson, 28, is reported to have attached a pillow round his waist to avoid being injured by razor wire.
He was serving a 12-year sentence for armed robbery.
He is reported to have escaped after cutting through a gate at the back of a small secure exercise yard attached to his cell.
"He was able to get out of that exercise yard and then he had a range of bed sheets that he tied together and was able to swing them over the wall to then effect his escape by scaling that wall," New South Wales Corrective Services Commissioner Peter Severin told ABC News.
"It appears that he also had a pillow [that was] put around his waist and enabled him to make good his escape over the razor wire."
Commissioner Severin said Jamieson had a history of trying to escape and was put into solitary confinement after a man-made hole was discovered inside a workshop at the prison.
"He was clearly somebody that was in maximum security for all the right reasons and furthermore he was actually segregated in the maximum security section," he said.
The commissioner said that the escape was "a very serious matter" and would be the subject of an intensive security review because there was "absolutely no excuse for anybody being able to escape from maximum security".
A huge manhunt for Jamieson is now under way.
Two people have been arrested after a man suffered head injuries in an serious attack in County Down.
[NEXT_CONCEPT]
One man was killed and two people were injured in a crash involving three lorries and a car on the M40.
[NEXT_CONCEPT]
Plymouth Argyle are preparing for Saturday's derby against Exeter with some warm-weather training in Spain.
[NEXT_CONCEPT]
A maximum security prisoner has staged an audacious escape in the Australian state of New South Wales by tying bed sheets together to climb over a wall.