Final answer:
The research method in question is naturalistic observation, where psychologists or researchers observe behavior in natural contexts without intervention.
Step-by-step explanation:
The type of research being used when a psychologist studies the play behavior of third-grade children by watching groups during recess at school is known as naturalistic observation. This method involves observing subjects in their natural environment without any manipulation or intervention by the researcher. A key example in psychology would be when researchers observe children on a playground to understand their social interactions, being careful to remain unobtrusive to not affect the children's behavior.
An example from anthropology is the work of Jane Goodall, who famously used naturalistic observation to study chimpanzees in their natural habitat. In both human and animal studies, the objective is to observe authentic behavior in a natural setting, allowing for the collection of valuable data about social structures, interactions, and other behaviors.