Police believe Jason was trying to stop an argument with a partygoer who had asked three gatecrashers to leave when he was slapped twice to the head by one member of the trio who was holding a long, sharp object, believed to be a screwdriver.
The 17-year-old was then punched by a second gatecrasher before the trio fled.
Friends have told police Jason seemed dazed and had a trickle of blood coming from his forehead.
Rachael Donaldson, the mother of the 16-year-old girl celebrating her birthday on the night Jason was attacked, said she had put a bandaid on the boyâs head after the altercation