One who infiltrates an organization or territory; an undercover or covert agent.
A person who secretly watches and examines the actions of other individuals or organizations and gathers information on them (usually to gain an advantage).
A defensive player assigned to cover an offensive backfield player man-to-man when they are expected to engage in a running play, but the offensive player does not run with the ball immediately.
To act as a spy.
To search narrowly; to scrutinize.
To explore; to see; to view; inspect and examine secretly, as a country.
To spot; to catch sight of.