Footage has emerged of football fans brawling at Swansea City's away match to Bristol City on Saturday.
Police and Ashton Gate Stadium say they are investigating disorder within the ground involving both sets of fans.
Swansea City say the club is "extremely disappointed to witness reports of anti-social behaviour at Bristol City", while police said "a large group of Swansea fans seem to have arrived in Bristol with the intention of drinking to excess and seeking confrontation".
A statement from the stadium says: "Up to 800 visiting fans arrived at the stadium 20 minutes after kick-off and immediately removed the segregation nets on the east corner of the Atyeo Stand.
"The situation was initially dealt with by the stewarding team and police in the vicinity. Twenty-five Swansea City fans were removed during the game and there were a number of arrests.
"Regrettably, several Bristol City supporters were involved in altercations in the corner of the Atyeo Stand and Dolman Stand before being apprehended."
The stadium say two stewards and a police officer had to be treated for minor injuries, while they are prepared to ban any home or away supporters behind the "unpleasant experience".
Avon and Somerset Police say they are looking into "attempts at co-ordinated disorder and incidents of criminal damage before, during and after" Bristol's 2-0 win over the Swans.
A man from Swansea who was arrested for alleged assault was later released without charge. Police say there were no arrests in the ground.
Chief Superintendent Paul Mogg said: "It is very disappointing that a large group of Swansea fans seem to have arrived in Bristol with the intention of drinking to excess and seeking confrontation. There was disorder within the ground, with objects thrown by each group of supporters.
"There was further disorder after the match in Ashton Park and officers were deployed with dogs and horses to separate the two groups of fans.
"We’ve also had reports of damage at least two pubs. These and any other offences which are disclosed will be thoroughly investigated."
A Swansea City spokesperson said: "The club is extremely disappointed to witness reports of anti-social behaviour at Bristol City.
"To take 3,300 fans to an away fixture contributes fantastic support for Graham Potter and the team and we would like to thank the majority of those supporters who travelled.
"Unfortunately, it is the remaining small minority from both clubs who have made the headlines for all the wrong reasons, which is deeply regrettable.
"We will work with all the different authorities to investigate the matter, while maintaining our zero-tolerance policy towards anyone found guilty of anti-social behaviour."
Ashton Gate Stadium managing director Mark Kelly said: "Ashton Gate Stadium has a very strong record of match day safety and I can assure our fans that any home or away supporters that caused this unpleasant experience will be banned.
"The incident in its entirety was captured on CCTV and a formal investigation in conjunction with the Avon and Somerset Police match commander and our head of safety is under way."
Anyone with information which could help the investigation is asked to contact police online, or call 101, quoting reference 228 of Saturday 2 February.
