The people involved have been warned they could face lifetime match bans after fighting broke out, bottles were thrown and a gate ripped open.
The violence happened during the interval of the Championship match on Saturday afternoon which West Brom drew 1-1 with Millwall at home.
One of the brawls was captured on a video shared on social media and shows punches and kicks being thrown as a blue gate separating home and away fans is torn down.
Others can be seen making a break for it to escape the ugly scenes as a crowd storms the fence.
Bottles and cans are thrown in both directions and among the violence is a man lying on the floor, apparently unconscious, as drinks land around him.
Some Baggies fans stood around the man in an attempt to protect him from the violence as others shout "We are Albion".
One steward can be seen in the video but no police are present.
Chief Inspector Ian Gorman, from West Midlands Police, said the force was now working with the club to track down those responsible.
He said: "We’re sad to say that there were pockets of fighting at the match on Saturday.
"Video of some of these fights was uploaded onto Facebook and Twitter which we’re using along with our own images and the club’s CCTV to find those responsible.
"People found guilty of crimes at fixtures face lifetime match bans as well as the sentences handed down by the courts.
"Anyone who can help our investigation into violence at the West Brom v Millwall game should contact us via Live Chat on our website west-midlands.police.uk."
West Bromwich Albion confirmed they were working with police and Millwall Football Club as they pledged anyone responsible would receive "appropriate punishment".
A spokesman for the club said: "We are aware of an incident which took place during the interval of yesterday’s fixture against Millwall, and a full review has begun in conjunction with West Midlands Police.
"We will work with police and Millwall Football Club to ensure anyone responsible for the disorder receives the appropriate punishment."
The fighting has been condemned on social media, with one supporter posting: "We all know that not all football fans are like this.
"Both ‘sides’ will claim the other one started it. That doesn’t make it right, sad to see these scenes to be honest."
Whilst another added: "Sickening violent scenes. Hope the person is ok."