Officers were called to the disturbance in Armthorpe this morning to discover the 15-year-old suffering from serious injuries sustained in the incident.
A South Yorkshire Police spokesman said: “Police received a call at 8.21am this morning following reports of a fight taking place on Gunhills Lane in the Armthorpe area.
“Officers attended and a boy, aged 15, was found with injuries believed to have been inflicted with a metal bar.
"The boy was transported to hospital by the ambulance service, and has since been discharged.
One man, aged 27, was arrested on suspicion of grievous bodily harm, and has been bailed while enquiries continue.
Anyone with information which may assist officers is asked to call 101 quoting incident number 199 of 24 March.
Alternatively, you can contact Crime Stoppers on 0800 555 111.