Mix butter, light corn syrup, light brown sugar, and vanilla extract over stovetop on medium heat.
While caramel is cooling, air pop large bowl of popcorn and remove all un-popped kernels. You don't want to bite down onto those hard pieces later while enjoying the chewy caramel popcorn ball.
Pour desired amount of caramel over popcorn so that it completely covers popcorn and mix thoroughly.
Cover your hands in butter and then grab large handful of caramel popcorn and press firmly into ball. Place on wax paper or baking sheets.