Spotter

Noun

 * 1) A person who observes something.
 * 2)  A member of a sniper team.
 * 3)  A person who keeps watch of the person performing an activity, in order to help them should they be unable to complete it.

Thesaurus
Argus, CIA man, Charley, airplane spotter, beagle, cloak-and-dagger operative, counterintelligence agent, counterspy, dick, double agent, espionage agent, eye, fire patrolman, fire warden, fireguard, flatfoot, forward observer, gumshoe, gumshoe man, hawkshaw, inside man, intelligence agent, lookout, lookout man, military-intelligence man, naval-intelligence man, night watchman, operative, patrol, patroller, patrolman, picket, private eye, reconnoiterer, roundsman, scout, secret agent, sentinel, sentry, skip tracer, sleuthhound, spy, spy-catcher, tec, undercover man, vedette, watch, watcher, watchkeeper, watchman

Derived terms

 * planespotter/plane spotter
 * train spotter
 * weather spotter

Anagrams

 * potters
 * protest

Noun

 * 1) jeerer; mocker