A teenage boy has been injured after an item was thrown into a section of the crowd at Portman Road during the Ipswich Town vs Sunderland game at the weekend.
The incident happened in the lower Sir Bobby Robson Stand just before kick-off on Saturday, December 18.
A spokesman for Suffolk police said: "A male suspect threw the unknown object which struck and injured a supporter."
Anyone with information or who has video footage which could help officers with their enquiries is being asked to contact Suffolk police, quoting the crime reference number 37/71757/21.
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