Jousting

From Halopedia, the Halo Wiki

Jousting is the act or gametype in multiplayer in Halo 3 where two Mongoose vehicles are driven towards each other, the rider in back will have either an Energy Sword, Shotgun, or Gravity Hammer. when they draw close they will attack each other, the surviving team is the winner. It can also be used when two mongooses go off the opposite man cannons at the same time on narrows. The passengers are both armed with a Spartan Laser, and if correctly done only one pair will survive to land on the other side. However, sometimes both teams die due to neither shot hitting, and both teams plummeting to their death.