>>216344004
It's the Ashura procession observed on the 10th day of the Muharram, by Shia Muslims, all over the world.
It's in remembrance of Ali's struggle and his brutal killing.
They do self-flagellation as a symbolic gesture of identifying with his pain, both physically and psychologically.

It's quite a brutal sight to see, as Sunni or a non-muslim, the streets are flowing with blood.