A 16-year-old boy needed hospital treatment after being found with a head injury inside the Tesco Alliance on Broad Street yesterday evening (27 July).
He was discharged earlier today.
Police say a group of youngsters were involved in 'an altercation' inside the store at 7:25pm.
Five people have been arrested and bailed pending further enquiries.
The incident is being treated as a grave and criminal assault.
Anyone with information on what happened is asked to call police on 612612 or Crimestoppers anonymously on 0800 555 111.