Both Rotherham United and Millwall have today released statements regarding the crowd trouble that occurred during the pair's Championship match at the New York Stadium on Saturday.
Police are investigating several incidents that happened both during the match and on the day of the game, including clashes when Rotherham scored a winner in the final 10 minutes.
Rotherham said on their website that some Lions fans travelled North with the "intent on causing disorder".
The Millers' statement read: "We were aware that a section of Millwall supporters were planning on attending this game intent on causing disorder. Contingency plans were in place to deal with this outcome with extra stewarding and police resources in place to deal with the anticipated threat.
"Despite the extra resources deployed this group made numerous attempts to seek disorder throughout the afternoon resulting in the despicable scenes towards the end of the match.
"Rotherham United are angered and upset at the unprecedented level of violent behaviour of some sections of the Millwall supporters inside and outside of the stadium. We are liaising closely with South Yorkshire Police to identify the individuals involved and our teams are already analysing all of our CCTV footage."
Millwall followed Rotherham with a statement of their own that said they would assist the Millers and the police and ban anyone found guilty of disorder.
"The club's position remains clear - anyone associated with the club found guilty of violent behaviour will be banned from Millwall matches, in addition to any punishment they receive from the authorities," read the statement.