Combat Game Mode (combat) is the sort of begginer mode of Natural Selection.
The easiest way to disguniush a Combat map from a Classic map is the map name will begin with 'co_'. e.g. co_faceoff
In Combat neither team can build structures without a plug-in being used.
Both teams spawn in rounds of people, which means that a number of Marines could just appear in the Marine Start suddenly, trapping an Alien. This is also a disadvantage though, as if all the Marines were killed, then the Aliens could have some time, without resistance, attacking the Marine's Command Chair or Armoury. However, Marines do not need Infantary Portals and just spawn near their Command Chair, which is another advantage as the Aliens cannot see where the Marines will be spawning from.
The Aliens can only have one hive in Combat. This is at a set place, which helps the Marines as they know exactly where the Aliens will start.
The overview of the map is not avaliable and cannot be used in this mode. pressing the default 'c' button will not do anything.