Dancing Hunter glitch
From Halopedia, the Halo wiki
The glitch occurs when a Hunter becomes suddenly unaware of the player's location, yet is being told by the game to attack them immediately. Because the Hunter can not determine where the player is, they shift back and forth, constantly changing direction until they discover where the player is. This most commonly occurs during Firefight, where the Hunter may have just killed the player and is waiting for them to respawn.
The dancing may or may not affect the Hunter's bond brother if they are still alive, and even then one might break out of it faster than the other.