Martyrdom

Martyrdom is a tier-three perk that automatically causes the player to drop a live grenade upon death. The grenade cannot be cooked as you never hold it, but a Martyrdom grenade's fuse is only 2.5 seconds (opposed to the 5 second fuse of a grenade used more conventionally). If you are already holding a grenade while you die, you leave behind both the grenade you were holding and the Martyrdom perk grenade.

The perk is very useful in close quarters levels, as well as small rooms where it is difficult for the enemy to exit in time to escape the blast. In multiplayer, some servers ban the use of Martyrdom, either for it being considered cheap, or that it can become annoying if many/all of the players on a server have it. Although many also argue that the inclusion of this perk and weapons such as the M16 are simply part of the game and can be easily avoided by more experienced players.

If you are quick to react, it can be very advantageous to throw an enemy's martyrdom grenade if the grenade was just dropped, as you do not need to run away and risk exposing yourself to fire, and you can get kills with it. It is commonly considered a very "cheap" and "noobish" perk to use. Though probably a joke for the developers to ward off people attempting to "teabag", it is thought extremely ridiculous that a player using it can be rewarded for dying. On the PC verison of the game, it is rare to find a player not using the perk, probably because the common server having at about 40 or 50 players. With that high number, it is no exaggeration that on Free-For-All servers, especially on smaller maps such as Vacant or Shipment, players using it will get half of the total kills they earned from the perk. On the XBOX 360 and PS3 verisons of the game, Martydom is being used less and less, probably because of it now being rare to get a kill with the perk. With most players very used to avoiding the perk, it can be traded in for a more useful third tier perk.

Additional Multiplayer Tactics
Not a reliable perk but one that may give a player a handful of additional kills. Most players now will assume that a player has Martyrdom and flee the area as soon as they achieve a kill. Confined areas and Sonic Boom makes this perk more effective. Be ready to sprint and/or move backward once an opponent is eliminated. If you are extremely close to the fallen, it is better to push forward and escape that way. If there is a threat of running toward more enemies then try move around a corner or go prone behind something. Turning completely around may take too long and there is a good possibility you will be hung up on another teammate. It should be noted that some servers will kick players using this perk in the PC version of Call of Duty 4.