The Hustle was a line dance popular in Los Angeles (and across the country) in the mid-seventies. Music producer, Van McCoy came up with a song to go with the dance, and "The Hustle" made it to #1 on the Billboard Hot 100 the week of July 26, 1975.
However, 'hustling' or 'doing the hustle' was more than just a song and dance in L.A.'s working class neighborhoods in those days. It was also a way of life, and hustling was a term commonly used to describe doing whatever it took to bring in additional income. Today, we would call it being entrepreneurial.