Place a 12-ounce glass in the freezer for 15 minutes.
Add ice cream balls to the glass and slowly fill with hard cider or sparkling cider. Allow foam to subside and add more cider.
Sprinkle the cinnamon on top of the float.
To make the floats melt more slowly OR if serving a crowd, pre-freeze ice cream balls on a parchment-lined baking sheet the night before.