According to reports in the British media, the trouble occurred in the Real Betis section, which threw objects - including lit flares - at the disabled section of the stands.
There, among other things, an eight-year-old autistic boy was hit by a thrown coin, but escaped relatively unscathed.
- Even before the match had started, they threw lighters, coins and packets of handkerchiefs and plastic cups.
They threw everything possible at us.
But it was when our third goal went in that it got really uncomfortable.
Then they jumped over the barriers and threw things.
A coin hit my son in the back of the head, the mother of the eight-year-old boy told the Manchester Evening News, continuing:
- He has special needs and that is why we sat in the disabled section.
We go to all the matches.
There were a lot of people in wheelchairs and everyone had things thrown at them.
It was absolutely terrifying.
I support rivalries, but this was completely gratuitous.
They threw beer and everything.
Manchester Police confirm that a police officer has been injured by a flare, and that four Betis supporters have been arrested for violent opposition, possession of pyrotechnics and possession of drugs.