Instagib is a gameplay mode in the online multiplayer FPS called Quake Live.
All weapons, armors, powerups, health kits, and holdable powerups will be removed, and every player is equipped with Gauntlet and Railgun! Your opponent will die if you hit him with either Gauntlet or Railgun. But don't let them hit you and you have to wait to respawn. You can use Gauntlet when you are in close quarters combat.