Three fans were arrested after trouble flared in the stands following the final whistle in the 0-0 first-leg match between Huddersfield and Millwall at the Galpharm Stadium. Officers with batons entered the Millwall section of the ground as bottles were thrown on to the pitch and between the two sets of supporters.
One Millwall fan was taken from the stand with what appeared to be blood on his face.
A spectator, who did not want to be named, said: "It kicked off in the Millwall end behind the goal. They started lobbing bottles and things and they all rushed to the bottom corner, where the Huddersfield fans were.
"The Huddersfield fans were also throwing stuff back at them and it all got a bit ugly.
"The police stopped it fairly swiftly by forming a cordon and pushing the Millwall fans back up the stand."
A West Yorkshire Police spokesman said: "There was an outbreak of minor disorder at today's Huddersfield Town versus Millwall game, where police had to draw batons to secure order at the ground. The disorder was quickly brought under control."
The spokesman said three Millwall fans were arrested for public order offences.