Yesterday was May 1st, also known as International Workers's Day or May Day in Montreal. The anti-capitalist group CLAC announced that they intended to “disrupt commercial activity dominated by the local bourgeoisie (...) in an attempt to destroy capitalism.”
Like most protests in Montreal, the message is unclear, the desired results aren't achieved and the situation quickly turned chaotic and violent.
The crowd started launching colored smoke grenades, fireworks and paint bombs at Montreal police on Sainte-Catherine Street West, so they obviously responded by launching smoke grenades and tear gas to disperse the crowd.
Spoiler alert: Capitalism was not overthrown this day!