In a medium saucepan over medium-high heat, combine sugar, water, syrup, vinegar, butter, and salt. Cook, stirring occasionally, until mixture reaches 260° (hard-ball stage) on a candy thermometer, about 10 minutes.
Transfer popcorn to a large bowl, drizzle syrup over, add nonpareils, and toss gently to coat.
When mixture is cool enough to handle, press popcorn into 3" balls with lightly greased hands.
Cool completely before serving.
Recipe by 5* trending recipes with videos at https://food.theffeed.com/2019/12/10/popcorn-balls/