Wash. Rev. Code § 51.12.150
Any musician or entertainer who performs as a member of a group or recognized entity is deemed an employee of the group or entity and the leader of the group or entity shall be required to properly register as an employer with the department and pay industrial insurance premiums on behalf of his or her employees. If a musician or entertainer is a sole performer or performs as a partner in a group or entity, or performs on a casual basis, the musician or entertainer shall be exempted from mandatory coverage of this title. However, any such sole performer, partner, or casual performer may elect to be covered under this title and shall be subject to all the provisions and entitled to all the benefits under this title.
RCW 51.12.150
Employments excluded-Musicians and entertainers: RCW 51.12.020.