” Free lance.
Why is an independent writer, photographer, or the like called a ‘free lance’?

A medieval mercenary soldier who was free of any continuing loyalties was known as a ‘free companion.’ Sir Walter Scott in his novel ‘Ivanhoe,’ coined a more descriptive term for such a soldier–‘free lance.’ “

–from the Dictionary of Word Origins: A History of the Words, Expressions and Cliches We Use by Jordan Almond, Citadel 1997