I gave the actual definition of it already. Both the left or right can be fascist. Most of the actual governments that fit the definition of fascism are communist or socialist. Some of that is written by left leaning academics.
Antifa's beliefs and actions fits the definition of fascism better than the people they are against.They are against free speech completely. They use violence and intimidation against the people who they disagree with politically. Alot of them believe in communism. Their name is oxymoronic and just serves as misdirection.
Both the right and left can be authoritarian but fascism is specific to the right just like stalinism is uniquely left wing