Violence briefly erupted at Fratton Park last night after a Southampton fan sat among Pompey supporters.
Stewards moved quickly to quell the disturbance in the main Fratton End of the ground.
The incident happened on the hour mark of Pompey’s 1-1 draw against Morecambe.
Fans sitting near the top of the Fratton End said fighting started when a man took off his coat to reveal he was wearing a red and white shirt - the colours of Pompey’s traditional rivals.
Some said that he had waved a Southampton FC banner.
As the man was attacked - with some fans who witnessed the incident saying that he was punched and stamped on - stewards raced to the top of the Fratton End to restore order.
The man was restrained and swiftly ejected from the ground while a red and white scarf he had been wearing was thrown around the Fratton End.
A short video clip of the incident widely circulated on social media showed the man wearing a red and white polo shirt.