A garda was attacked by a group of men as he attempted to arrest a man in the early hours of Sunday morning.
The garda, stationed in Dundrum, south Co Dublin, suffered serious injuries after the assault by up to seven men.
The garda and a colleague were giving chase, on foot, to two men after a suspected stolen car was abandoned in Ballinteer.
The man ran to the front door of a house where the garda was trying to arrest him when it is understood that a number of men came out of the house and began to beat up the garda.
It is understood he was stabbed in the leg and beaten about the head.
The incident happened around 6am. Other gardaí came on the scene a short time afterwards and two arrests were made.
The Garda Press Office said two males aged 18 and 20 were arrested and confirmed that an investigation has begun into the theft of a car, public order incidents and the assault on the garda.
The injured garda, who is in his 30s, is being treated for suspected concussion and lacerations.