Were you looking for Deathmatch? Critical Ops changed the name of the gamemode.
Critical Strike Portable
Players can be spawned in random places and are usually found spread across the map. Players can also infinitely kill any enemies and when killed, they respawn in 5 seconds (unless settings are changed). This gamemode has no legitimate objective, other than to simply kill each other and raise their kill count. Once a player reaches 50 kills before anyone else, he/she gets a gold metal and earns $2000.