There should be a weapon that does no damage, just used for tactical purposes. The rounds would slow your target down, including movement, reloading, aiming, switching weapons, throwing grenades, etc. It should also work on vehicles. To fire it, you'd need to charge it for the same amount of time as the Rail gun. It would be a UNSC weapon. There should also be a similar weapon for the Forerunners that would impair your vision.