Police responded to a fight that broke out at 1 a.m. on Monday between a group of men and members of a residence in the northeast of Guelph.
The people involved were known to each other and the incident was not random and possibly related to an earlier interaction where a man, 18, was struck by a vehicle.
The 18-year-old Guelph male was taken to Guelph General Hospital with serious injuries and later transported to a trauma centre.
The Guelph Police Service Traffic unit, Forensic Identification unit and Investigative Services are investigating. Anyone with information are asked to contact police.