spotter

noun7

1. •
   A person who observes something.
2. •
   A member of a sniper team who in addition to this function is responsible for providing additional information about targets from a different point of view.
3. •
   (US) A person who gives directions for a crane or vehicle (that is challenging to navigate) from a different point of view to the moved load.
4. •
   A team member responsible for communication with the driver to keep them up-to-date about on-track events, such as other nearby cars.
5. •
   A person employed to assist a sports presenter by identifying the players or events during a game.
6. •
   One who supervises a person performing an activity, in order to help them should they be unable to complete it.

   • Due to a spotter's lack of action in holding the weight when a lifter lost her balance, the lifter badly pulled some muscles. — 1981
7. •
   Dolphins of the genus Stenella, and specifically Stenella attenuata distinguished from the streaker (Stenella coeruleoalba) and the spinner (Stenella longirostris).