This happens so much, it's not uncommon for two players to kill each other by meleeing at the same time. The tactic doesn't have an official name I could find, so let's call it the shoot-melee combo. Melee is best used in conjunction with your gun: a tried-and-true strategy of the past 20 years of Halo is to whittle an enemy's shield down to near-zero with bullets and then finish them off with a single melee strike. One gun smack will take out your entire shield, and two hits is always death. More than any other FPS around, a lot of Halo fights begin or end with a melee attack. Halo's other combat pillar is the melee attack.
