Used other than figuratively or idiomatically: see in, field.
Actively engaged in fighting or dealing with the enemy; in battle or on maneuvers.
Away from the office, classroom, or laboratory; working with people or things in their natural environment.
In a real-world setting, as opposed to the controlled conditions of a laboratory or the hypothesized parameters of a theoretical approach.
Used other than figuratively or idiomatically: see on, the, ground.
Directly in an area of interest or active operations; in the field.