Blur Field

You select a point within range of the spell affecting a 60 feet sphere. All creatures within the sphere or attacks into the sphere have disadvantage on their attack rolls unless they possess true sight for the duration.

Concentration for this spell is optional. If you do not wish for the spell to have concentration when you cast it, it doesn't for the duration. This means that it doesn't end your concentration if you are already concentrating on a spell. If you do wish for the spell to have concentration you can, for the duration, move the sphere within a point within range for the duration with a bonus action.