Ventilar's spell punish

Choose a point you can see. A 15 foot radius sphere envelopes any creature within the sphere's area. No spells can be cast within the sphere, and if a creature attempts to cast a spell, they take 1d10 force damage for each level of the spell ( cantrips deal 1d6 damage). For an example, a wizard inside the sphere attempts to cast the lightning bolt spell. Because the wizard is inside the sphere, the spell does not continue and the wizard takes 3d10 damage. Weapons and spells have no effect on the sphere from inside or outside.