There were a few reports of violence, including one journalist being hit on the leg with a baton after running past police whilst on a mobile phone.
Footage showed the arrested being led into a police station, one man screams as if he is being hit once inside the station. He was handcuffed at the time and arm locked.
The Global Social Forum demonstration gathered at Kirov stadium at 2pm.
Over 200 police were drafted in, and positioned themselves behind the the large metal gates that have been closed since activists entered the stadium.
Military were also spotted by this journalist outside, behind the police.
The demonstration was refused permission to leave the stadium. No one was arrested and the protest dispersed back into the stadium an hour later.