A 54-year-old fisherman suffered a fractured jaw and fractured ribs after being assaulted by a group of youths in Hilsea on Thursday.
Police have reported that a group of youths attacked the man whilst he was fishing.
The incident took place underneath a footbridge crossing the M27, near Perrone Road, Hilsea, between 4pm and 4:45pm.
The police are appealing for information in their search for the suspects.
A spokesman from Hampshire Constabulary said: 'The group of males are believed to be white and between 14-18 years old.
'One suspect has dark hair and was wearing a white t-shirt.
'Another was of a chubby build, with long messy browny, blonde hair.'
A female cyclist stopped to help the fisherman, who required hospital treatment.
Police are hoping to identify the cyclist to find out more information about the case.
Anyone with more information is asked to call 101, quoting reference 44190280708.