Spotter
A person who watches a rope scene for signs of trouble and is ready to help, often asked for in self-suspension, performances and ties that are new or higher-risk for the rigger.
A spotter watches over a rope scene, looking for warning signs, and steps in to help if something goes wrong. Anatomie Studio’s rope vocabulary notes that many scenes do without one, but that a rigger trying something new or riskier may ask one or more people to spot, and it calls spotters highly advisable for self-suspension and for performances. English Wikipedia’s article on suspension bondage also mentions spotters as extra hands for lowering the person if something goes wrong, and points out that getting someone out of a suspension is difficult if they lose consciousness or a winch or hoist jams. See also emergency release.