Player corpses walking
Player corpses walking is a rare bug which prevents players in a deathmatch game from fully respawning, causing them to become mobile corpses. They have 100% health, but cannot pick up objects or use weapons, nor can they be attacked. The affected player's field of vision remains at ground level.
This phenomenon has been observed in a map whose deathmatch starting points were too close to the walls (in which case the engine tries to respawn players at co-op starting points instead), and which contained no co-op starting points.