Where does the shag haircut come from?

The answer

The shag grew out of the shaggy, layered looks of the 1970s, when haircuts moved away from stiff set styles toward something freer. It has returned in different forms many times since, each revival adapting it, so there is no single definitive version. Some versions lean soft, some sharp and edgy, and some blend with other cuts such as the mullet or the wolf cut.