The concept of Expected Points (EP) in football traces back to 1970 when Virgil Carter used the 1969 season to estimate the value of plays. Expected Points Added (EPA) is a way of bringing context to the number of yards gained or lost on a particular play. But how is EPA calculated? Are there different versions? And how can you build your own version of this and other models? In this workshop we'll address some of the foundations of modern football analytics and talk about how the assumptions made in the construction of both play by play and Next Gen Stats (NGS) models can have profound impacts on results that influence everything from player selection to coaching decisions.