A total of eight people have been arrested after police were assaulted by away supporters during Aston Villa’s Europa League win over Young Boys at Villa Park.
Supporters of the Swiss side threw items, including broken seats and coins, at Villa players and police officers, with Dutch forward Donyell Malen being struck on the head.
The disorder broke out during the first half of the tie, which Villa won 2-1.
Officers said two away fans were arrested on suspicion of affray and assaulting a police officer, while a further six were later arrested at Birmingham Airport.
Superintendent Paul Minor said: "We won't tolerate violence of any kind at football matches.
"The majority of the crowd was in good spirit, but unfortunately, a small minority of away fans caused violence and disrupted the game.
"An investigation has been launched, and officers are reviewing body-worn video and CCTV from the stadium of the disorder."
UEFA's Disciplinary Body will assess reports from Villa Park before deciding on any potential next steps.
The violence broke out in the lower tier of the Doug Ellis Stand when Villa took the lead and dozens of police officers were deployed in riot gear.
The unrest continued following Villa's second goal, with more items being thrown at Malen.
Young Boys captain Loris Benito went over to the supporters to try and calm the situation, but the unrest heightened as fans collided with police officers at the scene, with punches and seats being thrown.
Some of the fans were ejected as the game resumed several minutes after the second goal had been scored.
There were no further issues in the second half.
When asked about the trouble in the stands, Villa head coach Unai Emery said: "We need respect for both sides. It is not necessary to get a moment like we had today. Respect for both sides. I think he's (Malen) OK."
Young Boys were fined ÂŁ24,729 for similar issues involving their supporters at Manchester City two years ago and around ÂŁ15,756 for the use of pyrotechnics at Celtic in February.
SportNews' Rob Jones at Villa Park:
"For the first 40 minutes of the game it was pretty good-natured. The Young Boys fans were making a good noise. There was plenty of energy but the mood on that side of the stadium changed when Aston Villa scored their opening goal.
"Donyell Malen scored and then ran across towards the Young Boys fans but not in an antagonistic way. He wasn't that near but as he ran to that side of the ground a host of things were thrown from the visiting supporters and one of them clearly hit Malen on the head.
"He finished the half after scoring a second goal with a clear cut on his head which had drawn blood.
"He scored the second goal and ran towards the same side of the ground but nowhere near the Young Boys supporters. They tried their best to throw something but he was too far away.
"After that happened, it became a lot more heated between the stewards inside the ground and the Young Boys fans. Initially it was plastic cups being thrown but after that there were at least two or three pale blue seats that were thrown by Young Boys supporters.
"After that there was a delay in the game as the stewards came together with the supporters who were at the right of the front of that stand and two or three supporters were ejected.
"It was pretty unsavoury, the scenes we saw."
Young Boys head coach Gerardo Seoane said:
"I think it's normal when you score a goal that you want to celebrate with your teammates. Maybe it was a small provocation, I don't know. Our fans maybe took this like a provocation, but I think this is part of the football, our fans should not react so heavily.
"The referee asked our captain to go to our supporters, and he was going there to calm a bit, and I think some supporters came down to have a talk, and the police reacted like they would jump into the pitch, but it was not their intention, this is what I know, and I think they reacted a bit early.
"It's a pity for everybody, for the provocations, for throwing the object, for thinking that somebody would jump on the pitch, and I think the result is not nice for anybody, and for sure we apologise. We don't feel good.
"The way our supporters are normally, it is not how we want to act when we are guests somewhere, and I think nobody wins at the end, everybody loses with this situation."
