Twelve people were arrested during crowd trouble at the FA Cup fourth-round tie between Hull and Millwall on Saturday.
Supporters at the KC Stadium reported seeing seats ripped out and used as missiles as a section of Millwall fans tried to get to their Hull rivals at two stages during the match.
Police in riot gear quickly joined stewards to deal with the trouble which first broke out before the kick-off in a corner of the North Stand where the away fans were closest to Hull supporters in the East Stand.
In the second half, a further incident was spotted in the other corner of the North Stand which was packed with Millwall supporters who had made the trip from London.
At the end of the match, which ended as a 2-0 victory for the home side, police horses patrolled the touchline as thousands of Millwall fans were kept behind by the police.
Some of those in the 18,639 strong crowd said the atmosphere was tense from the start when Hull paraded their new £5 million signing Jimmy Bullard on the pitch. The former Fulham player was met by a chorus of boos from the Millwall fans.
Humberside Police confirmed 12 fans had been arrested and were still in custody in the city.
A spokesman said he believed the operation to counter the violence had worked well as officers and stewards prevented the two sets off supporters coming together in the ground.
He thought 30 or 40 seats had been ripped out during the match.
Millwall manager Kenny Jackett said: "There were one or two rushes and then towards the end of the game you see the police horses come out. I don't think it was off-putting for us."
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