Six arrests were made following crowd trouble in Saturday's Championship match between Birmingham City and Millwall.
A 30-year-old man was arrested on suspicion of assault after a 60-year-old Millwall fan was seriously injured near to St Andrew's stadium shortly before 3pm, when the match kicked off.
The victim, who is believed to have been with his family, was treated at the scene and taken to hospital. West Midlands Police confirmed that five more people were arrested following the match and that "bricks, bottles and objects were used as weapons".
A report from the BBC claims that around 150 seats inside the stadium were also vandalised during the game. Images and videos of clashes between opposing fans within the ground emerged yesterday on social media.
In a statement, West Midlands Police said: "The level of violence - which our officers put themselves in the middle of to protect people - meant some of our officers had to wear public order helmets, use shields and draw their batons, while continually warning people to move away.
"We understand how the scene may have scared people who had nothing to do with the violence. Bricks, bottles and objects were used as weapons in the hotspots around Digbeth and other areas between the stadium and New Street railway station.
"Our Football Policing Unit and detectives from Force CID have opened a joint investigation. They are working closely with both football clubs and supporter groups. More arrests will come in the following weeks meaning anyone involved should immediately go to their local police station to explain what happened."
A spokesperson from Millwall said: "The club is assisting the police and other authorities with their investigation into disorder involving both sets of supporters following the conclusion of Saturday's game. Any individual found guilty of such offences will receive an indefinite ban from home and away matches."
Birmingham City have been contacted by Mirror Football .
Millwall boss Gary Rowett, a former Birmingham manager, said he was aware of some crowd trouble during the game.
He said: "I'll be really honest, I could see something, I couldn't see whether it was both fans or just one set of fans or whatever it was. I am sure both clubs will look at it and deal with it. It's certainly not something you want to see at the end of a football match, my daughter is in the away end so you don't want to see that. That's up to the clubs to see what happened and get a bit of clarity on that."
The game saw the Lions twice come from behind to seal a 2-2 draw in an entertaining contest that keeps alive their hopes of gatecrashing the Championship play-off spots.
Juninho Bacuna's opener for the hosts was cancelled out by Oliver Burke in the second half. Then, a penalty from Lyle Taylor looked like it would seal all three points for Birmingham only for Benik Afobe to convert a spot-kick of his own in the 96th minute to ensure spoils were shared. Millwall stay seventh but are now three points behind Sheffield United who occupy the final play-off spot with two games to go.
Rowett added: "What we have got is fabulous desire and character. We ended up with Oliver Burke at right wing-back, Tyler Burey at left wing-back and Jake Cooper up front on his own. Maybe, just because of that, we deserved something out of the game."
