Caltrops

You cause caltrops to appear from the ground in a 5-foot square area within range; the caltrops last for the duration. Any creature that moves into the spell’s area must make a Dexterity saving throw against your spell save DC. On a failed save, the creature stops moving and takes 1 piercing damage.

Taking this damage reduces the creature's walking speed by 10 feet until the creature regains at least 1 hit point. A creature moving through the area at half speed doesn't need to make the save.