Communists dont believe in private property, therefore they will steal from those that do, and theft to my knowledge always happens with force and violence.
Just an aside, you are obviously confusing theft with robbery. You may think the difference in meaning is minuscule (or irrelevant), but, for example, the judicial system (the judgment of which should be of particular interest to you) greatly distinguishes between them...
And there is a reason behind that
It can be both. You can see shoplifting threads on reddit, full of leftists, which steal from poor small shop owners, ideologically driven. It's disgusting