Hundreds of young people responded to a call by supporters of two YouTube rivals to gather at Alexanderplatz, a large square in central Berlin, where a mass brawl erupted, police in the German capital said on Friday.
“Around 400 people gathered on the square early on Thursday evening,” a police spokesman said.
A report in the Berliner Morgenpost newspaper indicated that the fracas originated in a conflict between Stuttgart rapper Thatsbekir, who has around 260,000 followers, and Bahar Al Amood from Berlin, with 13,000 followers.
Both sides invited their supporters to Alexanderplatz for Thursday evening, sending out the invitations ahead of time, with indications that a punch-up was pending.
A fight then erupted involving around 50 people, who started hitting and kicking each other and using pepper spray, police said. Videos of the fracas were later posted on the internet.
Around 20 from the group then ran into the nearby subway station, jumped onto the rails and began throwing stones taken from the track ballast. Order was restored by around 9:30 pm (2030 GMT).
Police deployed around 100 officers and detained nine people, using teargas to quell the disturbance, according to the spokesman. An order was called out over police loudspeakers for the youths to clear the square. Two officers were slightly hurt.
Police have opened 13 investigations for causing bodily harm and serious disturbance of the peace.
Berlin police have identified seven crime hotspots in the capital, one of which is Alexanderplatz, known to residents simply as “Alex” with its iconic TV tower.