In the last 100 years there have been loads.
The Kingsmill Massacre is the first one that springs to mind, carried out by the Provisional IRA with their political wing the Socialist Sinn Fein in the background.
The IPLO were unashamedly hardline left-wing socialists too. Pretty sure they shot up a Protestant boozer which included fatalities.
North Korea and China are particularly brutal left-wing regimes. Check their human rights records.
Then you've got AntiFA who run about the USA with baseball bats. Pretty sure their violent 'protest' as Berkely involved them trying to burn down the place. Tons of examples of these cowards lashing out at Trump supporters or anyone they deem not to be 'woke'
There are countless other examples.