Hardcore

Hardcore mode is an alternative to the normal playlists in Call of Duty 4: Modern Warfare, Call of Duty: World at War, and Call of Duty: Modern Warfare 2. As the name suggests, the gameplay is much more serious, with the following implications:
 * Significantly less health - Players can only withstand 30% of the damage they could in normal modes before dying or going into Last Stand.
 * Limited HUD - Nothing in the way of displays shows unless a UAV/Recon Plane is called, in which the map in the upper left appears. It promptly disappears when it expires. Since players are not notified when they are over a dropped weapon they could pick up, weapon stealing seldom occurs. Exceptions to this include green text ID'ing teammates, a symbol that you are carrying the bomb in Hardcore Search and Destroy, or the display of flags in Hardcore War and of the HQ location in Hardcore Headquarters. In the hardcore Wii version of Call of Duty: World at War, there is a white dot used as a reticle in the game. In Modern Warfare 2, all notifications (upper right corner of the screen) of players calling/destroying killstreaks or achieving match targets or triple kills are disabled. There are two exceptions to this: players will be notified if someone copies their class or if someone destroys their tactical insertion.
 * Friendly fire on - Teammates can be killed just as easily as enemy players. If this happens, the same point total earned for a kill is deducted from the teamkiller's score, although at the end of the game such penalties are not included. Deliberate teamkillers are punished; in Call of Duty 4, a player is automatically killed and sat out for a period of time after 3 or more teamkills. In Call of Duty: World at War, a player is removed from the game entirely after three teamkills, excluding those from artillery or bouncing betties. Modern Warfare 2 returns to the same rules as Call of Duty 4, but friendly fire penalties are sometimes harsher (as much as 3 minutes for a RPG teamkiller at the beginning of the round). Also, if a friendly fire penalty is triggered while using an AC-130 or Chopper Gunner, the killstreak will end.
 * Hardcore Ricochet - In Modern Warfare 2, Hardcore Ricochet game modes replace Hardcore versions of Search and Destroy and Headquarters, where instead of teamkills occurring with friendly fire, the player committing the friendly fire takes the same damage he inflicted on the teammate, which could mean getting killed. Team Deathmatch is the only game mode in Modern Warfare 2 with normal Hardcore rules.
 * Killcam - In Modern Warfare 2, a killcam is not shown to the player after death. This benefits players who like to be stealthy and hide in concealed locations, since it will not be made immediately obvious to the victim where his enemy was. Theoretically, a well concealed marksman could stay hidden for an entire game, although the view will still zoom in on the killer afterwards.

Game modes available
In Call of Duty 4 In Call of Duty: World at War In Call of Duty: Modern Warfare 2
 * Hardcore Team Deathmatch
 * Hardcore Search and Destroy
 * Hardcore Headquarters
 * Hardcore Team Deathmatch
 * Hardcore Search and Destroy
 * Hardcore War
 * Hardcore Headquarters
 * Hardcore Free-for-All
 * Hardcore Team Deathmatch
 * Hardcore Ricochet: S&D
 * Hardcore Ricochet:HQ Pro

Exclusion in Call of Duty: World at War
As mentioned above, a player is removed from the game after three teamkills, with the exception of artillery, bouncing betties, or if a bomb they planted in Search and Destroy kills a teammate. If this happens the player will also not be able to re-join the game session by joining the players in progress. However, the host player cannot be kicked, due to the game's inability to host migration during game. However, much like Call of Duty 4, the host player will be killed off and sat out of the game for a period of time.

Announcement
When a player gets booted from the game, regardless of whether or not it was a teammate or enemy player, the game's announcer will make a statement, even if it is the host player who doesn't actually get kicked. There are two such statements for each of the four factions players can play as:

Red Army: Wehrmacht: Marine Raiders: Imperial Army:
 * Cowards and traitors will be dealt with, severely!
 * Such a man has no place in this army!
 * A teammate has disappointed the Führer! You will not see him again!
 * Your teammate has disgraced us all. He will be dealt with, harshly!
 * He ain't fit to wear the uniform!
 * Get that son of a bitch out of here!
 * A teammate has abandoned the path of the warrior!
 * He brings only shame to his family!

Trivia

 * In MW2, Hardcore can be used as a resource to get weapon attachments that otherwise would be difficult to achieve. For example, the sniper rifles with silencers would (in core) be almost impossible to get a one shot kill with; in Hardcore, it becomes easy. It is also easy to receive XP from perk challenges, as Stopping Power is not needed.
 * In MW2, many people use Hardcore as an easy way to unlock Extended Mags since only 2+ shots through cover is needed to take down a target, compared to 3-4+ in Core.
 * Though there is no UAV Recon, a player will have a little mini map on their wrist most of the time. It does not help though.
 * Hardcore is the most realistic gametype in the Call of Duty series since there is nothing that tells you how much ammo you have, who's winning a battle, and so on. The only thing that is not real is the Spawn Delay. Once your player is dead, they're dead.