Young Boys fans clash with police during Europa League match at Villa Park
Play was temporarily stopped in the first half
Aston Villa's Europa League victory over Young Boys was marred by trouble from the away support at Villa Park.
A positive night for Villa - which gave them a seventh straight home win - was tarnished by trouble from travelling fans, who have a history of causing problems.
Donyell Malen struck a first-half brace but that resulted in home players being pelted by objects thrown by visiting supporters.
The goalscorer suffered a cut to the head after he was caught by a flying plastic cup.
Orchestrated clapping and singing turned ugly when Young Boys fell behind and the game was stopped for five minutes as fans clashed with police in the Doug Ellis Stand and even needed captain Loris Benito to calm them down.
Dozens of police officers were deployed in riot gear in front of the away end and no further trouble occurred after the interval.
Young Boys supporters were fined 28,250 euros for similar issues at Manchester City a couple of years ago and around 18,000 euros for the use of pyrotechnics at Celtic in February.
The action on the pitch played second fiddle for a while and Joel Monteiro's late consolation did not stop Villa from earning a fourth win from five in the competition as their superb form continued.
Villa were keen to assert their authority from the first whistle and Malen's effort from range inside four minutes looked destined for the back of the net, only for goalkeeper Marvin Keller to tip the ball over the crossbar.
The home side made the pressure count and grabbed the opening goal in the 27th minute.
Youri Tielemans collected the ball on the edge of the area and had time and space to lift it onto the head of Malen who guided the ball beyond Keller.
In the aftermath of the goal, Malen and his team-mates went to celebrate in front of the away support and objects were thrown towards them. Malen came away from it sporting a cut to the head.
The hosts were going through the gears and had their second three minutes before the break. Morgan Rogers played a neat pass to Malen who cut inside and dispatched expertly into the back of the net.
Like his first celebration, Malen went towards the away fans and missiles were again thrown which caused clashes with police and the referee to stop the game for five minutes.
On the pitch, Villa continued to boss proceedings.
They thought they had a third when a long ball over the top was played to Rogers and he squared to Malen who thought he had a hat-trick, but the assistant flagged for offside to cut celebrations short.
Young Boys looked to have halved the deficit when Alan Virginius played the ball across for Chris Bedia to convert, but, after a lengthy VAR review, the goal was disallowed for offside in the build-up.
The visitors did get their goal in the 90th minute when Monteiro latched onto a pass from Gregory Wuthrich and slammed into the back of the net, but Villa held on despite late pressure.
Villa boss Unai Emery did not have much to say when asked about the ugly scenes in the first half but felt they were "not necessary".
He added: "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 boss Gerardo Seoane apologised for fans' behaviour but admitted they may have been provoked by the Villa players celebrating in front of them.
Seoane also said fans came down from the stand to speak to the players but police thought they were attempting to jump onto the pitch, which caused chaos.
"It's normal when you score a goal that you want to be with your team-mates. Maybe it was a small provocation, I don't know," he said. "Our fans could have taken this as a provocation.
"This is part of football but our fans should not react so angrily.
"The referee asked our captain to go calm our supporters. Some fans came down to talk to the players and the police reacted like they were jumping on the pitch, but that was not their intention.
"It's a pity for everybody throwing the objects. The result is not nice for anybody.
"We apologise, we don't feel good and not the way our supporters are normally, or how we want to act when we are guests somewhere and no one wins at the end, everybody loses in this situation.
"Football is with emotions. There is a rule to not provoke, nobody does it on purpose, it was more the joy of scoring."