Have you ever seen a door labeled Restricted? If so, you probably know it means "Stay out." A restricted area can only be entered by certain people.
Anything labeled restricted is not public. Restricted things are private, and only certain people who are authorized can access or use those things. Anything restricted is subject to more rules. In sports, a restricted free agent has to worry about more rules than an unrestricted free agent. Something or someone restricted has to deal with restrictions, which are rules or laws that set limits.