Rod of the Disciplinarian

This black lacquered wooden rod is banded in steel, has a fanged head, and functions as a magic mace. As a bonus action, you can brandish the rod at a creature and demand it refrain from a particular activity—attacking, casting, moving, or similar. The activity can be as specific (don’t attack the person next to you) or as open (don’t cast a spell) as you want, but the activity must be a conscious act on the creature’s part, must be something you can determine is upheld or broken, and can’t immediately jeopardize the creature’s life. For example, you can forbid a creature from lying only if you are capable of determining if the creature is lying, and you can’t forbid a creature that needs to breathe from breathing.
The creature can act normally, but if it performs the activity you forbid, you can use a reaction to make a melee attack against it with the rod. You can forbid only one creature at a time. If you forbid another creature from performing an activity, the previous creature is no longer forbidden from performing activities.