Police were called to the Greenfields site in Braybrooke late on Sunday evening (July 10) after reports of a serious disturbance.
One man remains in police custody, after two who had earlier been arrested were released on bail.
Eyewitnesses said that the site had now been deserted, with vehicles with what looked like bullet holes and smashed windows left behind.
A Northamptonshire Police spokesman said: “Police were called late on Sunday night following reports of a serious disturbance at the Greenfields travellers site in Braybrooke.
Truck driver dies after crash near Northamptonshire border
Who's been sentenced from Kettering, Raunds and Wellingborough
A14 collision leads to traffic jams near Kettering
Meet 105-year-old Marjorie - who must be Kettering's oldest property landlady
Corby company's home town pride leads to name change
“As a result of that incident, a 17-year-old male is currently in a stable condition in hospital after being treated for what are believed to be shotgun injuries.
“A number of individuals were questioned by police at the scene and two men were initially arrested, but later released on police bail.
“One further male remains in police custody at this time.
“Our inquiries are ongoing at this stage and we would ask anyone with information about the disturbance, which began at about 11pm on Sunday, to contact police on 101 or Crimestoppers, anonymously, on 0800 555111.”