Away fans were prevented from entering the stadium after objects were thrown at officers, West Midlands Police say.
Four police officers have been injured and 46 people are in custody after “disgusting and highly dangerous scenes” before Aston Villa’s game with Legia Warsaw.
West Midlands Police said fans of the Polish side were not allowed into the stadium after missiles were thrown at officers before the start of the Europa Conference League game on Thursday evening.
The visiting fans were held in the coach park near the ground, while officers faced “90 minutes of sustained violence”.
Stewards also removed several people believed to be away supporters from the home stands during the match, while footage on social media appeared to show objects being thrown into the stadium from outside.
A safety advisory group recommended that the ticket allocation for away fans be cut by a thousand after trouble at Legia Warsaw’s match against AZ Alkmaar in the Netherlands in October.
The force’s assistant chief constable, Damian Barratt, said this was not “taken well by the club”, with fans turning up to pick up tickets that were not there for them.
“The away fans were in an area that was identified as a ticket collection point, we were seeking to facilitate their safe entry with tickets,” he told Sky News.
“That became unsustainable and unachievable because we couldn’t maintain the same safety because they didn’t have tickets.”
He said the mood “quickly changed” when it became clear tickets were not going to be issued to all fans – and they “turned their attention onto the police officers”.
“That quickly escalated into the throwing of missiles. Those missiles were hard objects, they were flares,” he said, adding he was proud of the efforts made by officers to control the disorder.
“One of our officers was injured as a result of being struck by a flare and suffered both a burning of clothes and smoke inhalation as a result of that,” he said.
